Implements support for binary-number syntax ("0b10")

Resolves https://github.com/facebook/hhvm/issues/1425.

Some remarks:
- My C/C++ is rather rusty, I'm thankful for every comment :-)
- I'm not so sure if there are more places which need a "compatibility-upgrade"  for the binary-syntax. I ran the slow and quick test-suites, but I'm afraid that does not give much information.
- There is probably a a more elegant way to solve `hphp/parser/hphp.ll line 662`