Add Subversion::esc helper function

All paths passed to the svn command line tool should go through this function. Presently the only thing it does is to append a ‘@’ to the filename if the filename already contains one. This is required because subversion cuts any suffix matching /@[^@]*$/ and treats that as shorthand for the revision argument (-r).

Ideally svn would have an option to disable this behavior.
Remove all calls to ‘rescan project’

This is a no-op with TextMate 2.0.
Allow ‘@’ in filenames for Add, Commit, and Log

Doing a complete fix (for all commands) is very complicated as there is no ideal place to add this escaping.

Ideally we would escape at the level where we pass the paths to ‘svn’, but the current API simply provide an argument array that may contain things other than paths, and the commit window can also call ‘svn’ (e.g. for add and diff).

Given the decreased use of subversion and the rarity of ‘@’ in paths, I don’t think it’s worth investing the time to overhaul the bundle to better handle this issue.

Fixes #5.