Revision 665193

Thrift: More constant enums.

Summary:
Make enum constants as structure defaults work.
Make enum constants as constant map keys work.
Un-break the generated skeleton servers.

Reviewed By: mcslee

Test Plan:
cd test
../compiler/cpp/thrift -cpp ConstantsDemo.thrift
g++ -I../lib/cpp/src -c gen-cpp/*.cpp
Also compared the generated output to the old generated output.

Revert Plan: ok