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

.travis.yml

@@ -78,7 +78,7 @@ before_install:
         FORMULA=$1
         SHA=$(brew fetch --force $FORMULA 2>&1 | grep ^SHA256: | cut -d ' ' -f 2)
         sed -E -i.bak "s/sha256 \"[0-9a-f]{64}\"/sha256 \"$SHA\"/g" \
-          /usr/local/Library/Taps/homebrew/homebrew-binary/$FORMULA.rb
+          "$(brew --repository homebrew/homebrew-binary)/$FORMULA.rb"
       }
       brew update --quiet
       brew tap homebrew/binary --quiet