Changed GIT_REMOTE_DOWNLOAD_TAGS_ALL to behave like git 1.9.0
Merge pull request #2673 from swisspol/2672

Fixed GIT_REMOTE_DOWNLOAD_TAGS_ALL to behave like git 1.9.0+
Rename git_threads_ to git_libgit2_

This describes their purpose better, as we now initialize ssl and some
other global stuff in there. Calling the init function is not something
which has been optional for a while now.