Switched the NameGenerator to a static counter instead of a random suffix

This ensures that the doubler does not generate duplicate class name even
when the generation runs too fast for the entropy source.
Closes #38
Replaces #64 by avoiding to slow down the library artificially because of
md5.
Merge pull request #73 from stof/static_counter

Switched the NameGenerator to a static counter instead of a random suffix
Changed the way to check for Closure::bind to support HHVM