Allow installation to proceed when CLT is dispersed

@benhoskings commit message should say it all. mind cutting a release with this?
```bash
~ ln -s /usr/local/bin/gcc-4.8 /usr/local/bin/gcc
~ babushka 'xcode tools'
xcode tools {
  These commands run from more than one place.
  'cc', 'c++', 'g++', 'clang', 'make', 'ld' & 'libtool' run from /usr/bin, but 'gcc' runs from /usr/local/bin.
  Multiple installations might indicate a problem. Meet anyway [n]? y
  Install Xcode via the App Store, then go Preferences -> Downloads -> Components -> Command Line Tools.
  I don't know how to fix that, so it's up to you. :)
  You can view a more detailed log at '/Users/tamird/.babushka/logs/xcode tools'.
~
```