"env grep" - add support for regular expression matches

When CONFIG_REGEX is enabled, the new option "-e" becomes available
which causes regular expression matches to be used.  This allows for
example things like these:

- print all MAC addresses:

	=> env grep -e eth.*addr
	eth1addr=00:10:ec:80:c5:15
	ethaddr=00:10:ec:00:c5:15

- print all variables that have at least 2 colons in their value:

	=> env grep -v -e :.*:
	addip=setenv bootargs ${bootargs} ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}:${netdev}:off
	panic=1
	eth1addr=00:10:ec:80:c5:15
	ethaddr=00:10:ec:00:c5:15
	ver=U-Boot 2013.04-rc1-00289-g497746b-dirty (Mar 22 2013 - 12:50:25)

etc.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/cmd_nvedit.c b/common/cmd_nvedit.c
index 9158b96..f8dc38e 100644
--- a/common/cmd_nvedit.c
+++ b/common/cmd_nvedit.c
@@ -165,12 +165,13 @@
 		       int argc, char * const argv[])
 {
 	char *res = NULL;
-	int len, grep_flags;
+	int len, grep_how, grep_what;
 
 	if (argc < 2)
 		return CMD_RET_USAGE;
 
-	grep_flags = H_MATCH_BOTH;
+	grep_how  = H_MATCH_SUBSTR;	/* default: substring search	*/
+	grep_what = H_MATCH_BOTH;	/* default: grep names and values */
 
 	while (argc > 1 && **(argv + 1) == '-') {
 		char *arg = *++argv;
@@ -178,14 +179,19 @@
 		--argc;
 		while (*++arg) {
 			switch (*arg) {
+#ifdef CONFIG_REGEX
+			case 'e':		/* use regex matching */
+				grep_how  = H_MATCH_REGEX;
+				break;
+#endif
 			case 'n':		/* grep for name */
-				grep_flags = H_MATCH_KEY;
+				grep_what = H_MATCH_KEY;
 				break;
 			case 'v':		/* grep for value */
-				grep_flags = H_MATCH_DATA;
+				grep_what = H_MATCH_DATA;
 				break;
 			case 'b':		/* grep for both */
-				grep_flags = H_MATCH_BOTH;
+				grep_what = H_MATCH_BOTH;
 				break;
 			case '-':
 				goto DONE;
@@ -197,7 +203,7 @@
 
 DONE:
 	len = hexport_r(&env_htab, '\n',
-			flag | grep_flags | H_MATCH_SUBSTR,
+			flag | grep_what | grep_how,
 			&res, 0, argc, argv);
 
 	if (len > 0) {
@@ -1153,8 +1159,12 @@
 	"env flags - print variables that have non-default flags\n"
 #endif
 #if defined(CONFIG_CMD_GREPENV)
+#ifdef CONFIG_REGEX
+	"env grep [-e] [-n | -v | -b] string [...] - search environment\n"
+#else
 	"env grep [-n | -v | -b] string [...] - search environment\n"
 #endif
+#endif
 #if defined(CONFIG_CMD_IMPORTENV)
 	"env import [-d] [-t | -b | -c] addr [size] - import environment\n"
 #endif
@@ -1200,8 +1210,15 @@
 U_BOOT_CMD_COMPLETE(
 	grepenv, CONFIG_SYS_MAXARGS, 0,  do_env_grep,
 	"search environment variables",
+#ifdef CONFIG_REGEX
+	"[-e] [-n | -v | -b] string ...\n"
+#else
 	"[-n | -v | -b] string ...\n"
+#endif
 	"    - list environment name=value pairs matching 'string'\n"
+#ifdef CONFIG_REGEX
+	"      \"-e\": enable regular expressions;\n"
+#endif
 	"      \"-n\": search variable names; \"-v\": search values;\n"
 	"      \"-b\": search both names and values (default)",
 	var_complete