Merge branch 'gb/split-cmdline-errmsg'

* gb/split-cmdline-errmsg:
  split_cmdline: Allow caller to access error string

cache.h

@@ -1099,6 +1099,8 @@ void overlay_tree_on_cache(const char *tree_name, const char *prefix);
 
 char *alias_lookup(const char *alias);
 int split_cmdline(char *cmdline, const char ***argv);
+/* Takes a negative value returned by split_cmdline */
+const char *split_cmdline_strerror(int cmdline_errno);
 
 /* builtin/merge.c */
 int checkout_fast_forward(const unsigned char *from, const unsigned char *to);