Remove tab inserts when making JS file

On OS X, sed is super old and doesn't recognize \t, so the sed
commands in the Makefile end up prepending a bunch of literal 't'
characters to each line in the main Snowball.js file.
Add main Snowball.js file for inclusion in PX

Build and indent the main Snowball.js file so that we can use it in
the pxfe code without forcing everyone there to build.