Fixing compatibility with default CSS syntax file

There's a bug if the default CSS syntax file is loaded after this one,
it clobbers the regexes and creates buggy syntax highlighting.

Adding b:current_syntax stops the default css syntax file from
executing if it is loaded after this one.
Merge pull request #13 from amadeus/default-syntax-fix

Fixing compatibility with default CSS syntax file
Adding a couple pet extra CSS properties and highlight groups
Removing up old junk
Testing sync fromstart
Handling syntax sync from my vimrc