- mxodbc can use default execute() call

- mxodbc can use default execute() call
- modified SQLCompiler to support rendering of bind parameters as literal
inline strings for specific sections, if specified by the compiler
subclass, using either literal_binds=True passed to process() or any visit
method, or by setting to False the "binds_in_columns_clause" flag for SQL-92
compatible columns clauses..  The compiler subclass is responsible for
implementing the literal quoting function which should make use of the DBAPI's native
capabilities.
- SQLCompiler now passes **kw to most process() methods (should be all,
ideally) so that literal_binds is propagated.
- added some rudimentary tests for mxodbc.