INT64_MAX, INT64_MIN, possibly others, initialized wrong on OS X's ruby

[srh]

In lib/protobuf/message/field.rb, there's some constants set up like this:

      INT32_MAX  =  2**31 - 1
      INT32_MIN  = -2**31
      INT64_MAX  =  2**63 - 1
      INT64_MIN  = -2**63
      UINT32_MAX =  2**32 - 1
      UINT64_MAX =  2**64 - 1

The problem is that with OS X's ruby (on Mountain Lion, anyway), we get this:

$ /usr/bin/ruby -e 'puts 2**63'
-9223372036854775808

Yep. Its ruby can't do math good. The ruby --version is ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0].

It would be very nice if all these expressions were replaced by hard-coded integer literals.