Fix typos throughout codebase.

* NEWS:
* README:
* doc/r5rs/r5rs.texi:
* doc/ref/api-data.texi:
* doc/ref/api-debug.texi:
* doc/ref/api-evaluation.texi:
* doc/ref/api-io.texi:
* doc/ref/api-macros.texi:
* doc/ref/api-procedures.texi:
* doc/ref/api-scheduling.texi:
* doc/ref/api-undocumented.texi:
* doc/ref/libguile-concepts.texi:
* doc/ref/posix.texi:
* doc/ref/srfi-modules.texi:
* doc/ref/vm.texi:
* doc/ref/web.texi:
* examples/box-dynamic-module/box.c:
* examples/box-dynamic/box.c:
* examples/box-module/box.c:
* examples/box/box.c:
* examples/safe/safe:
* examples/scripts/README:
* examples/scripts/hello:
* gc-benchmarks/larceny/twobit-input-long.sch:
* gc-benchmarks/larceny/twobit-smaller.sch:
* gc-benchmarks/larceny/twobit.sch:
* libguile/expand.c:
* libguile/load.c:
* libguile/net_db.c:
* libguile/scmsigs.c:
* libguile/srfi-14.c:
* libguile/threads.c:
* meta/guile.m4:
* module/ice-9/match.upstream.scm:
* module/ice-9/ports.scm:
* module/language/cps/graphs.scm:
* module/scripts/doc-snarf.scm:
* module/srfi/srfi-19.scm:
* module/system/repl/command.scm:
* test-suite/tests/srfi-18.test:
Fix typos.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gc-benchmarks/larceny/twobit-input-long.sch

@@ -272,7 +272,7 @@
 (define (with-optimization level thunk) 
   (thunk))
 
-; Calls thunk1, and if thunk1 causes an error to be signalled, calls thunk2.
+; Calls thunk1, and if thunk1 causes an error to be signaled, calls thunk2.
 
 (define (call-with-error-control thunk1 thunk2) 
   (let ((eh (error-handler)))
@@ -21993,14 +21993,14 @@
 ;
 ; RS1 has an object.  If the tag of RS1 is not 'tag1', or if the tag is 
 ; 'tag1' but the header byte of the object header is not 'tag2', then an
-; exception with code 'excode' is signalled.  The exception call is set
+; exception with code 'excode' is signaled.  The exception call is set
 ; up to return to the first instruction of the emitted code.
 ;
 ; If RS1 is not RESULT then it is moved to RESULT before the exception 
-; is signalled.
+; is signaled.
 ;
 ; If RS2/IMM is not #f, then it is a register or immediate that is moved
-; to ARGREG2 before the exception is signalled; it is an immediate iff 
+; to ARGREG2 before the exception is signaled; it is an immediate iff
 ; imm? = #t.  
 ;
 ; RS1 must be a hardware register.

gc-benchmarks/larceny/twobit-smaller.sch

@@ -272,7 +272,7 @@
 (define (with-optimization level thunk) 
   (thunk))
 
-; Calls thunk1, and if thunk1 causes an error to be signalled, calls thunk2.
+; Calls thunk1, and if thunk1 causes an error to be signaled, calls thunk2.
 
 (define (call-with-error-control thunk1 thunk2) 
   (let ((eh (error-handler)))

gc-benchmarks/larceny/twobit.sch

@@ -272,7 +272,7 @@
 (define (with-optimization level thunk) 
   (thunk))
 
-; Calls thunk1, and if thunk1 causes an error to be signalled, calls thunk2.
+; Calls thunk1, and if thunk1 causes an error to be signaled, calls thunk2.
 
 (define (call-with-error-control thunk1 thunk2) 
   (let ((eh (error-handler)))
@@ -21993,14 +21993,14 @@
 ;
 ; RS1 has an object.  If the tag of RS1 is not 'tag1', or if the tag is 
 ; 'tag1' but the header byte of the object header is not 'tag2', then an
-; exception with code 'excode' is signalled.  The exception call is set
+; exception with code 'excode' is signaled.  The exception call is set
 ; up to return to the first instruction of the emitted code.
 ;
 ; If RS1 is not RESULT then it is moved to RESULT before the exception 
-; is signalled.
+; is signaled.
 ;
 ; If RS2/IMM is not #f, then it is a register or immediate that is moved
-; to ARGREG2 before the exception is signalled; it is an immediate iff 
+; to ARGREG2 before the exception is signaled; it is an immediate iff
 ; imm? = #t.  
 ;
 ; RS1 must be a hardware register.