Merge branch 'ls/travis-homebrew-path-fix' into maint

The procedure to build Git on Mac OS X for Travis CI hardcoded the internal directory structure we assumed HomeBrew uses, which was a no-no. The procedure has been updated to ask HomeBrew things we need to know to fix this. * ls/travis-homebrew-path-fix: travis-ci: ask homebrew for its path instead of hardcoding it