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

While creating this formula, I found to bugs in homebrew/binary:
* depends_on doesn't work for dependencies in homebrew/binary (breaks casperjs install)
* sha1 checksums aren't checked for devel (you can have `sha1 'foo'`and homebrew doesn't warn about it)