Handle execv() errors

Previously, awesome would just crash when execv() fails, because it already
destroyed all of its internal state, but then tries to do another main loop
iteration. Whoops.

Signed-off-by: Uli Schlachter <psychon@znc.in>

common/util.c

@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <limits.h>
 #include <fcntl.h>
+#include <errno.h>
 
 #include "common/util.h"
 
@@ -121,6 +122,7 @@ a_exec(const char *cmd)
         shell = "/bin/sh";
 
     execl(shell, shell, "-c", cmd, NULL);
+    fatal("execv() failed: %s", strerror(errno));
 }
 
 // vim: filetype=c:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80