Parse shorthand refspecs as valid

Relax the ONELEVEL ref naming rules so the refspec parsing code can
ask for 'master' to be considered valid.
remote: dwim the refspecs according to the remote's advertised refs

As git allows you to store shorthand refspecs in the configuration, we
need to do this ourselves.
push: don't send a packfile when only issuing delete commands

For update and create commands where all the objects are known to
exist in the remote, we must send an empty packfile. However, if all
we issue are delete commands, no packfile must be sent.

Take this into consideration for push.
travis: test push

Create a test repository in the VM and set up git-daemon so we can
use it to test the push code.
Merge pull request #1512 from carlosmn/push-delete-only

Fix push for delete-only and add travis rules to test it
cmake 2.6 parser bug workaround
Merge pull request #1513 from ethomson/cmake

cmake 2.6 parser bug workaround
don't use uninitialized struct stat in win32
Merge pull request #1516 from ethomson/win32_alternate_nostat

don't use uninitialized struct stat in win32
Merge pull request #1511 from carlosmn/refspec-shorthand

dwim shorthand refspecs for fetch