Bumped version number to 3.0.0pre
Fixed bug where Python-style comments were used in a bash script
Updated Thrift-generated Python classes for non-enum types

The major backwards-incompatible change between Concrete 2.0.x and
3.0.0 is the switch from using enums to represent types (Concrete 2)
to using strings to represent types (Concrete 3).

The Python files in this commit were auto-generated by the Thrift
compiler from the updated Concrete 3.0.0 thrift defintion files.  The
thrift definition files are stored separately, in the 'concrete'
repository on GitHub.