Fix an issue where DiffusionGitBrowseQuery incorrectly parses filenames with spaces

Summary:
Split from D1921. We'll explode each line into too many parts currently, if the filename contains spaces.

Also use -z to get \0 newlines.

Test Plan: Browsed a directory containing files with spaces in their names, links etc were correct.

Reviewers: nh, vrana, btrahan

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1924