brew.sh: Allow developers to specify curl/git paths
brew.sh: Allow developers to specify curl/git paths

This introduces the HOMEBREW_CURL_PATH and HOMEBREW_GIT_PATH
variables, which are used to populate HOMEBREW_CURL and HOMEBREW_GIT,
respectively, when in developer mode (HOMEBREW_DEVELOPER).

Both paths are expected to be valid executables and must
have the executable bit set.

claui/brew,DomT4/brew,claui/brew,JCount/brew,reitermarkus/brew,maxim-belkin/brew,EricFromCanada/brew,Homebrew/brew,maxim-belkin/brew,reitermarkus/brew,konqui/brew,Linuxbrew/brew,DomT4/brew,DomT4/brew,nandub/brew,Homebrew/brew,Linuxbrew/brew,reitermarkus/brew,vitorgalvao/brew,nandub/brew,JCount/brew,EricFromCanada/brew,DomT4/brew,nandub/brew,konqui/brew,vitorgalvao/brew,sjackman/homebrew,JCount/brew,JCount/brew,Homebrew/brew,Linuxbrew/brew,mahori/brew,Homebrew/brew,mahori/brew,konqui/brew,vitorgalvao/brew,MikeMcQuaid/brew,sjackman/homebrew,reitermarkus/brew,EricFromCanada/brew,claui/brew,konqui/brew,Linuxbrew/brew,MikeMcQuaid/brew,mahori/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,maxim-belkin/brew,EricFromCanada/brew,vitorgalvao/brew,nandub/brew,sjackman/homebrew,claui/brew,mahori/brew,sjackman/homebrew