move phantomjs and casperjs to binary, add formula for slimerjs and add slimerjs support in casperjs

See mxcl/homebrew#22323 as reference

While creating this pull request, I found ~~two~~ a issue with homebrew/binary:
* ~~depends_on doesn't work for dependencies in homebrew/binary~~
   * `brew tap --repair` has fixed this (sry, first PR for taps) 
* sha1 checksums aren't checked for devel (you can have `sha1 'foo'`and homebrew doesn't warn about it

Should I report these issues to the main homebrew issue tracker (since taps are implementated there) or is this issue tracker the right place for it?