Make "clear" external command runnable without "!" and alias-able

Make the "clear" external command runnable without an exclamation point
("!") for convenient.  Additionally, make it acceptable as a command
string for alias exceptionally in external commands.

Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>

cmdline.c

@@ -1833,6 +1833,10 @@ allocate_alias(int origin)
 	if (get_command_table_entry(args[2])) 
 		found = TRUE;
 
+	/* Accept the "clear" external command exceptionally. */
+	if (STREQ(args[2], "clear"))
+		found = TRUE;
+
 	if (!found) {
 		if (!strlen(args[2])) {
 			if (alias_exists(args[1])) {

main.c

@@ -1043,7 +1043,8 @@ is_external_command(void)
             STREQ(cmd, "more") ||
             STREQ(cmd, "less") ||
 	    STREQ(cmd, "echo") ||
-            STREQ(cmd, "ls")) {
+	    STREQ(cmd, "ls") ||
+	    STREQ(cmd, "clear")) {
                 sprintf(command, "%s", cmd);
                 for (i = 1; i < argcnt; i++) {
                         strcat(command, " ");