Modification to truncate, add HAVE LO64 define.

Modify truncate to use lo_truncate64. Use HAVE_LO64 define to use new lo_*64 methods. Check size of offset and length for versions without LO64.

I have ran the tests with both 9.3 and 9.1, all pass.

This should be everything except for the version flag. I cannot figure out how to add the version flag based on where the version of postgres is calculated in the setup.py.