Revision 672907

Partial handlling of 64-bit integer constants.

- Parse integer constants in Thrift files as 64-bit ints.
- Die if an overflow occurs.
- Warn if an enum value cannot fit in 32 bits.
- Add a simple test for the above.

I ran all of the generators over BrokenConstants.thrift before adding the
overflow, and they appeared to work.  However, the code generated was not
always valid (for example, the 64-bit constant must have an LL suffix in C++).