Revert 999fa571 so timeouts do not kill client.

This reverts commit 999fa5713ac69e1617067dad7b47df6e5039115b.
Switch timeout handling to explicitly use INT_CANCEL since tdserror() converts INT_TIMEOUT to INT_CONTINUE
Merge pull request #179 from rails-sqlserver/revert_no_int_timeout

Revert 999fa571 so timeouts do not kill the client.