removed depreciated caching of git credentials, improved debian 7.7 support

fixes #207 

Since the code that was causing the issue on debian, seems to have been depreciated by handling credentials differently, I simply removed the function that was causing the issue rather than adding code to fix it.  So far with my limited installation tests on ubuntu 14.04, 12.04 and debian 7.7 this does not seem to have side effects.  At this point I thought it made sense to submit a pull request to get it running though TravisCI.  There may be other code that should be culled but at this point I believe this patch coupled with the bootstrap changes there is solid, even if unsupported, debian 7.7 compatibility.