I've introduced thrift_offset for a thrift_spec list. The change allows to use fastbinary module for structures with negative fields identifiers.
Can someone review my change? Issue: https://issues.apache.org/jira/browse/THRIFT-105 git branch: http://thrift-rpc.org/?p=thrift.git;a=shortlog;h=refs/heads/pri/shigin/py-newlib
