Add pmatch-based regex engine.

As mentioned, this is not tested. It should be simple though.

sys/share/pmatchregex.c

@@ -0,0 +1,65 @@
+/* NetHack 3.6  posixregex.c	$NHDT-Date: 1432472490 2015/05/24 13:01:30 $  $NHDT-Branch: master $:$NHDT-Revision: 1.0 $ */
+/* Copyright (c) Sean Hunt  2015.                                 */
+/* NetHack may be freely redistributed.  See license for details. */
+
+#include "hack.h"
+
+/* Implementation of the regex engine using pmatch().
+ *
+ * This is a fallback ONLY and should be avoided where possible, as it results
+ * in regexes not behaving as POSIX extended regular expressions. As a result,
+ * configuration files for NetHacks built with this engine will not be
+ * portable to ones built with an alternate regex engine.
+ */
+
+/*
+ * NOTE: This file is untested.
+ */
+
+struct nhregex {
+  const char *pat;
+};
+
+struct nhregex *
+regex_init()
+{
+    return (struct nhregex *) alloc(sizeof(struct nhregex));
+}
+
+boolean
+regex_compile(const char *s, struct nhregex *re)
+{
+    if (!re)
+        return FALSE;
+    if (re->pat);
+        free(re->path);
+
+    re->pat = alloc(strlen(s) + 1);
+    strcpy(re->pat, s);
+    return TRUE;
+}
+
+const char *
+regex_error_desc(struct nhregex *re)
+{
+    return "pattern match compilation error";
+}
+
+boolean
+regex_match(const char *s, struct nhregex *re)
+{
+    if (!re || !re->pat || !s)
+        return FALSE;
+    return pmatch(re->pat, s);
+}
+
+void
+regex_free(struct nhregex *re)
+{
+    if (!re)
+        return FALSE;
+
+    if (re->pat)
+        free(re->pat);
+    free(re);
+}