Re: [PATCH] start_command: close cmd->err descriptor when fork/spawn fails

> Fix the problem where the cmd->err passed into start_command wasn't 
> being properly closed when certain types of errors occurr.  (Compare the 
> affected code with the clean shutdown code later in the function.)
> 
> On Windows, this problem would be triggered if mingw_spawnvpe() failed, 
> which would happen if the command to be executed was malformed (e.g. a 
> text file that didn't start with a #! line).  If cmd->err was a pipe, 
> the failure to close it could result in a hang while the other side was 
> waiting (forever) for either input or pipe close, e.g. while trying to 
> shove the output into the side band.  On msysGit, this problem was 
> causing a hang in t5516-fetch-push.
> 
> I'm not sure why (or if) this problem hasn't cropped up under Linux. The 
> non-Windows code *does* try to check for execve() failures in the child, 
> in addition to the fork() failures.