GVFS Mount fails if post-command git hook outputs anything to stdout

Repro:

1. Add to user's .gitconfig:

[gvfs "clone"]
	default-post-command = D:\post-command2.hooks

2. Add D:\post-command2.hooks file with contents:

D:\post-command2.bat
3) Add D:\post-command2.bat hooks file with contents:

echo "blah"
4) unmount/remount repo.

5. see error:

D:\mono\src>gvfs mount
Authenticating...Succeeded
Failed to determine GVFS timeout and max retries: Error while reading 'gvfs.max-retries' from config: "blah"

Expected: gvfs mount should only fail if a git hook returns a nonzero exit code (or, I suppose, writes to stderr).

Note that this is not planned to be included in office's workflow, it's just something weird I found that I wanted to make sure was noted! Assigned to kevin because I found it while dogfooding gvfs sparse, but feel free to reassign as necessary as it's not exactly related!