Use seven characters instead of six for short SHAs -- this matches the short form of the command line and github.com
Merge pull request #71 from jspahrsummers/master

Use 7 characters instead of 6 for short SHAs
renamed repositoryURL => gitDirectoryURL and changed it to actually do what it says it does
gitDirectoryURL is strong
GTBranch.repository should be strong
Merge pull request #73 from libgit2/branches-should-retain-repositories

GTBranch.repository should be strong
Make GTReference.repository strong (similar to #73)
GTReference.git_reference should not be externally writable (since it will probably result in incorrect memory management)
Protect against multiple invocations of -[GTReference dealloc]
Merge pull request #74 from libgit2/refs-memory-management

Fixes to GTReference memory management
Always invalidate self.git_reference in -deleteWithError: (since git_reference_delete always will)
Invalidate self.git_reference if a rename fails
Merge pull request #75 from libgit2/gtreference-memory-management

Fix code that could result in invalid/freed references
++ libgit2
separate the additional description from the libgit2 description
update header docs
use git_branch_delete
Merge pull request #76 from libgit2/update-libgit2

++ libgit2
Merge pull request #77 from libgit2/better-branch-delete

Better branch delete
Merge pull request #78 from libgit2/better-errors

Better errors