Add 'for-humans?' flag to <language> specifications.

* module/system/base/language.scm (<language>): Add 'for-humans?'
  field, and export new 'language-for-humans?' predicate.

* doc/ref/compiler.texi (Compiler Tower): Document.

* module/language/assembly/spec.scm, module/language/bytecode/spec.scm,
  module/language/glil/spec.scm, module/language/objcode/spec.scm,
  module/language/tree-il/spec.scm, module/language/value/spec.scm:
  Mark these languages as 'for-humans?'.

doc/ref/compiler.texi

@@ -55,7 +55,8 @@ They are registered with the @code{define-language} form.
 @deffn {Scheme Syntax} define-language @
 name title reader printer @
 [parser=#f] [compilers='()] [decompilers='()] [evaluator=#f] @
-[joiner=#f] [make-default-environment=make-fresh-user-module]
+[joiner=#f] [for-humans?=#t] @
+[make-default-environment=make-fresh-user-module]
 Define a language.
 
 This syntax defines a @code{#<language>} object, bound to @var{name}

module/language/assembly/spec.scm

@@ -1,6 +1,6 @@
 ;;; Guile Virtual Machine Assembly
 
-;; Copyright (C) 2001, 2009, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2009, 2010, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -31,4 +31,5 @@
   #:parser      read ;; fixme: make a verifier?
   #:compilers   `((bytecode . ,compile-bytecode))
   #:decompilers `((bytecode . ,decompile-bytecode))
+  #:for-humans? #f
   )

module/language/bytecode/spec.scm

@@ -1,6 +1,6 @@
 ;;; Guile Lowlevel Intermediate Language
 
-;; Copyright (C) 2001, 2009, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2009, 2010, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -35,4 +35,5 @@
   #:printer	write
   #:compilers   `((objcode . ,compile-objcode))
   #:decompilers `((objcode . ,decompile-objcode))
+  #:for-humans? #f
   )

module/language/glil/spec.scm

@@ -1,6 +1,6 @@
 ;;; Guile Lowlevel Intermediate Language
 
-;; Copyright (C) 2001, 2009, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2009, 2010, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -37,4 +37,6 @@
   #:printer	write-glil
   #:parser      parse-glil
   #:compilers   `((assembly . ,compile-asm))
-  #:decompilers `((assembly . ,decompile-assembly)))
+  #:decompilers `((assembly . ,decompile-assembly))
+  #:for-humans? #f
+  )

module/language/objcode/spec.scm

@@ -1,6 +1,6 @@
 ;;; Guile Lowlevel Intermediate Language
 
-;; Copyright (C) 2001, 2009, 2010, 2011 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2009, 2010, 2011, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -79,4 +79,5 @@
   #:printer	write-objcode
   #:compilers   `((value . ,objcode->value))
   #:decompilers `((value . ,decompile-value))
+  #:for-humans? #f
   )

module/language/tree-il/spec.scm

@@ -1,6 +1,6 @@
 ;;; Tree Intermediate Language
 
-;; Copyright (C) 2009, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2009, 2010, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -42,4 +42,5 @@
   #:parser      parse-tree-il
   #:joiner      join
   #:compilers   `((glil . ,compile-glil))
+  #:for-humans? #f
   )

module/language/value/spec.scm

@@ -1,6 +1,6 @@
 ;;; Guile Lowlevel Intermediate Language
 
-;; Copyright (C) 2001, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2010, 2013 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -26,4 +26,5 @@
   #:title	"Values"
   #:reader	#f
   #:printer	write
+  #:for-humans? #f
   )

module/system/base/language.scm

@@ -25,7 +25,8 @@
             language-name language-title language-reader
             language-printer language-parser 
             language-compilers language-decompilers language-evaluator
-            language-joiner language-make-default-environment
+            language-joiner language-for-humans?
+            language-make-default-environment
 
             lookup-compilation-order lookup-decompilation-order
             invalidate-compilation-cache! default-environment
@@ -49,6 +50,7 @@
   (decompilers '())
   (evaluator #f)
   (joiner #f)
+  (for-humans? #t)
   (make-default-environment make-fresh-user-module))
 
 (define-macro (define-language name . spec)