Add support for POSIX regular expressions.

* regex-posix.c, regex-posix.h: New files. (Some code
is taken liberally from rx/rgx.c in the old Guile dist.)

* init.c: Include regex-posix.h.
(scm_boot_guile_1): Call scm_init_regex_posix.

* Makefile.am (EXTRA_libguile_la_SOURCES, modinclude_HEADERS):
Add regex-posix.[ch] sources.
* Makefile.in: Regenerated.

* scmconfig.h.in: Add HAVE_REGCOMP macro.  (automake is supposed
to do this automatically?  It didn't for me, bleh.)

libguile/init.c

@@ -81,6 +81,9 @@
 #include "pairs.h"
 #include "ports.h"
 #include "posix.h"
+#ifdef HAVE_REGCOMP
+#include "regex-posix.h"
+#endif
 #include "print.h"
 #include "procprop.h"
 #include "procs.h"
@@ -415,6 +418,9 @@ scm_boot_guile_1 (base, closure)
       scm_init_pairs ();
       scm_init_ports ();
       scm_init_posix ();
+#ifdef HAVE_REGCOMP
+      scm_init_regex_posix ();
+#endif
       scm_init_procs ();
       scm_init_procprop ();
       scm_init_scmsigs ();