since ARGBEGIN checks to see if argv0 is nil before assignment,
old commands can leave argv0 set.  since this is an on-stack value,
it is likely bogus.  fix to prevent crashes.

Reference: /n/atom/patch/applied/fossilboguserr
Date: Thu Apr  3 05:35:34 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/fossil/Ccli.c	Thu Apr  3 05:34:28 2014
+++ /sys/src/cmd/fossil/Ccli.c	Thu Apr  3 05:34:29 2014
@@ -33,6 +33,8 @@
 	return 0;
 }
 
+extern char *_argv0;
+
 int
 cliExec(char* buf)
 {
@@ -57,6 +59,7 @@
 			vtUnlock(cbox.lock);
 			if(!(r = cbox.cmd[i].cmd(argc, argv)))
 				consPrint("%s\n", vtGetError());
+			_argv0 = nil;		/* evade defn of ARGBEGIN */
 			vtMemFree(p);
 			return r;
 		}
--- /sys/src/cmd/fossil/9fsys.c	Thu Apr  3 05:34:33 2014
+++ /sys/src/cmd/fossil/9fsys.c	Thu Apr  3 05:34:35 2014
@@ -34,7 +34,7 @@
 	char*	curfsys;
 } sbox;
 
-static char *_argv0;
+char *_argv0;
 #define argv0 _argv0
 
 static char FsysAll[] = "all";