some work on syntax.test

* module/language/tree-il.scm (tree-il->scheme):
* module/ice-9/psyntax.scm (build-conditional): Attempt to not generate
  (if #f #f) as the second arm of an if, but it doesn't seem to be
  successful.

* module/ice-9/psyntax-pp.scm (syntax-rules): Regenerate.

* test-suite/tests/syntax.test (exception:unexpected-syntax): Change
  capitalization.
  ("unquote-splicing"): Update test.
  ("begin"): Add in second arms on these ifs, to avoid the strange though
  harmless expansion of `if'.
  (matches?): New helper macro.
  ("lambda"): Match on lexically bound symbols, as they will be
  alpha-renamed.

module/ice-9/psyntax.scm

@@ -368,7 +368,9 @@
     (case (fluid-ref *mode*)
       ((c) ((@ (language tree-il) make-conditional)
             source test-exp then-exp else-exp))
-      (else `(if ,test-exp ,then-exp ,else-exp)))))
+      (else (if (equal? else-exp '(if #f #f))
+                `(if ,test-exp ,then-exp)
+                `(if ,test-exp ,then-exp ,else-exp))))))
 
 (define build-lexical-reference
   (lambda (type source name var)

module/language/tree-il.scm

@@ -215,7 +215,9 @@
             `(,(tree-il->scheme proc) ,@(map tree-il->scheme args)))
 
            ((<conditional> test then else)
-            `(if ,(tree-il->scheme test) ,(tree-il->scheme then) ,(tree-il->scheme else)))
+            (if (void? else)
+                `(if ,(tree-il->scheme test) ,(tree-il->scheme then))
+                `(if ,(tree-il->scheme test) ,(tree-il->scheme then) ,(tree-il->scheme else))))
 
            ((<primitive-ref> name)
             name)