Merge branch 'jk/maint-cleanup-after-exec-failure'

* jk/maint-cleanup-after-exec-failure:
  git: use run_command() to execute dashed externals
  run_command(): help callers distinguish errors
  run_command(): handle missing command errors more gracefully
  git: s/run_command/run_builtin/

run-command.h

@@ -10,6 +10,7 @@ enum {
 	ERR_RUN_COMMAND_WAITPID_SIGNAL,
 	ERR_RUN_COMMAND_WAITPID_NOEXIT,
 };
+#define IS_RUN_COMMAND_ERR(x) ((x) <= -ERR_RUN_COMMAND_FORK)
 
 struct child_process {
 	const char **argv;