Correct reference counting of remotes

We were accidently overwriting the magic, causing the repository's
reference count to never be decremented.
Changes: update
xs: update libgit
Changes: update
v0.32

 - Update libgit2 to 648a985 (GH#53, GH#56) (thanks, @jacquesg!)
 - Minor Win32 build fix
 - Add Reflog class (GH#55) (thanks, @jacquesg!)
 - Suport non-default stash flags (GH#56) (thanks, @jacquesg!)
 - Clean-up test repositories after test run (GH#59) (thanks, @jacquesg!)
 - Rename classes (incompatible changes):
    + Git::Raw::TreeBuilder -> Git::Raw::Tree::Builder
    + Git::Raw::TreeEntry -> Git::Raw::Tree::Entry
 - Improve patch and diff support (GH#61) (thanks, @jacquesg!)
    + New classes: Git::Raw::Patch, Git::Raw::Diff::Delta,
      Git::Raw::Diff::Hunk, Git::Raw::Diff::File
 - Improve index conflicts handling (GH#62) (thanks, @jacquesg!)
 - Add support for filters (GH#57) (thanks, @jacquesg!)
 - Add support for blame (GH#63) (thanks, @jacquesg!)
 - Visual Studio build fixes (GH#64) (thanks, @jacquesg!)
 - Correctly handle Git::Raw::Remote refcount (GH#65) (thanks, @jacquesg!)