Add the path for the julia-installed git to the end of PATH, so that the system provided git is used if available.
Update git to 1.8.1.5 (there was a build failure in 1.8.1.4)
Bundle git's libexec
Set GIT_EXEC_PATH to the local installation when launching julia

Conflicts:
	Makefile
Merge branch 'master' of github.com:JuliaLang/julia
Avoid using hard links when installing git.