Potential fix for relative vs absolute path

Following instructions on pirate_game against Shoes4 master, found that the
bin/shoes script wouldn't run right. In particular, where we do a
`cd ./$NEXT_DIR` would fail when running against the aliased command pointing
to the gem installed binary.

I'm highly suspicious that there is either a better way to do this on OS X, or
that this won't be right when we finally get a gem-installable version of
shoes, but figured I'd put this out there while I was looking at it.
Merge branch 'master' into next_dir_problem_on_gem
Better link following on OS X

Works properly with alias to installed shoes per pirate_game as well.

Thanks @plexus!
Fixing link following on Mac
Deal with the perils of CDPATH
Merge pull request #520 from shoes/next_dir_problem_on_gem

Potential fix for relative vs absolute path