Allow installation to proceed when CLT is dispersed

@benhoskings commit message should say it all. mind cutting a release with this?
```bash
~ cat '/Users/tamird/.babushka/logs/xcode tools'
$ git rev-parse --git-dir
in dir /usr/local/babushka (/usr/local/babushka) {
.git
$ git rev-parse --short HEAD
in dir /usr/local/babushka (/usr/local/babushka) {
03243d8
babushka@03243d8 | /Users/tamird/.rvm/rubies/ruby-2.1.2/bin/ruby@2.1.2-p95
xcode tools {
  (defining xcode tools against external from /usr/local/babushka/deps/dev.rb)
  $ uname -s
  Darwin
  $ sw_vers
  ProductName:	Mac OS X
  ProductVersion:	10.9.3
  BuildVersion:	13D65
  setup not defined.
  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]  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'.
~
```