exposed vector clocks to the lua api

Ignore-this: 2dd48bdfcaf3ac48405b24578e390f85

darcs-hash:20140922014148-c21fe-32dfa5d2d406ba56ae37d606a140c5284f37f8ed
changing name to vclock instead of clock

Ignore-this: 110cf7c962f5e5b70cdf57c446ab2cb0

darcs-hash:20140922030805-c21fe-a82d549b54ce667b04dc1782ea8504602393908a