[pass] [bug] git add failing if file is below symlink

[Daniel Lublin]

Since we now support keeping symlinks down in the pass tree (tree(1)
output refinements were corrected for this case), I guess this must be a
bug.

When doing `pass edit` on a file that resides below a symlink, I'm getting:

  fatal: pathspec '/home/me/.password-store/foo-symlink/bar.gpg' is beyond a symbolic link

I think the solution is to resolve any symlinks in the `git_add_files()`
function. Of course, the use may do all kinds of sneaky things using these
symlinks, so resolving needs to be done with care hmmm.