error message when rehash fails on non-writable directory

Fixes #238
tests galore
configure Travis
skip Ruby stuff on Travis
use C on Travis for even less overhead
add hook lookup tests
fix resolving symlinks in rbenv-hooks
Don't duplicate shims in PATH
tests for rbenv-init
replace tab with spaces
Merge pull request #367 from shoyan/master

replace tab with spaces
Merge remote branch 'sstephenson/master' into develop

* sstephenson/master:
  replace tab with spaces
  tests for rbenv-init
  Don't duplicate shims in PATH
  fix resolving symlinks in rbenv-hooks
  add hook lookup tests
  use C on Travis for even less overhead
  skip Ruby stuff on Travis
  configure Travis
  tests galore
  error message when rehash fails on non-writable directory