Add support for POSIX character classes.

PR: 116826 (submitted by Roy Marples <uberlord@gentoo.org>)

Patch seems to be taken from dash, so probably a copyright
1997-2005 Herbert Xu <herbert@gondor.apana.org.au> is in order
(license is ok, the only GPL bit in dash is mksignames.c from
bash).

I also took a bugfix from dash (!!ccmatch because further
code assumes true is represented by 1).

diff --git a/expand.c b/expand.c
--- a/expand.c
+++ b/expand.c
@@ -1,6 +1,8 @@
 /*-
  * Copyright (c) 1991, 1993
  *	The Regents of the University of California.  All rights reserved.
+ * Copyright (c) 1997-2005
+ *	Herbert Xu <herbert@gondor.apana.org.au>.  All rights reserved.
  *
  * This code is derived from software contributed to Berkeley by
  * Kenneth Almquist.
@@ -1349,6 +1351,42 @@ patmatch(char *pattern, char *string, in
 }
 
 
+STATIC int ccmatch(char *p, int chr, char **r)
+{
+	static const struct class {
+		char name[10];
+		int (*fn)(int);
+	} classes[] = {
+		{ .name = ":alnum:]", .fn = isalnum },
+		{ .name = ":cntrl:]", .fn = iscntrl },
+		{ .name = ":lower:]", .fn = islower },
+		{ .name = ":space:]", .fn = isspace },
+		{ .name = ":alpha:]", .fn = isalpha },
+		{ .name = ":digit:]", .fn = isdigit },
+		{ .name = ":print:]", .fn = isprint },
+		{ .name = ":upper:]", .fn = isupper },
+		{ .name = ":blank:]", .fn = isblank },
+		{ .name = ":graph:]", .fn = isgraph },
+		{ .name = ":punct:]", .fn = ispunct },
+		{ .name = ":xdigit:]", .fn = isxdigit },
+	};
+	const struct class *class, *end;
+	char *q;
+
+	end = classes + sizeof(classes) / sizeof(classes[0]);
+	for (class = classes; class < end; class++) {
+		q = prefix(class->name, p);
+		if (!q)
+			continue;
+		*r = q;
+		return class->fn(chr);
+	}
+
+	*r = 0;
+	return 0;
+}
+
+
 STATIC int
 pmatch(char *pattern, char *string, int squoted)
 {
@@ -1434,6 +1472,15 @@ pmatch(char *pattern, char *string, int 
 					continue;
 				if (c == CTLESC)
 					c = *p++;
+				else if (c == '[') {
+					char *r;
+
+					found |= !!ccmatch(p, chr, &r);
+					if (r) {
+						p = r;
+						continue;
+					}
+				}
 				if (*p == '-' && p[1] != ']') {
 					p++;
 					while (*p == CTLQUOTEMARK)
diff --git a/mystring.c b/mystring.c
--- a/mystring.c
+++ b/mystring.c
@@ -88,14 +88,14 @@ scopyn(const char *from, char *to, int s
  * prefix -- see if pfx is a prefix of string.
  */
 
-int
+char *
 prefix(const char *pfx, const char *string)
 {
 	while (*pfx) {
 		if (*pfx++ != *string++)
 			return 0;
 	}
-	return 1;
+	return (char *)string;
 }
 
 
diff --git a/mystring.h b/mystring.h
--- a/mystring.h
+++ b/mystring.h
@@ -36,7 +36,7 @@
 #include <string.h>
 
 void scopyn(const char *, char *, int);
-int prefix(const char *, const char *);
+char *prefix(const char *, const char *);
 int number(const char *);
 int is_number(const char *);