[python-sybase] Patch for compiling with FreeTDS current

[hopfgartner <hop...@ro...>]

The following makes 2 changes in freetds.h:

1) The definition of CS_CLEAR is removed, since it's
defined in the FreeTDS headers.

2) The prototype of ct_commant got a const qualifier.

This enables compilation for FreeTDS current, as of
November 28.

Peter