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
fix iterating through paths that have spaces in them

Fixes #344, #196
add tests for exec
fix exec fails for invalid version
hack around the hack around bash `echo`
test completions for exec