C extension - fix reference leaks when converting int/long/float (to mysql)

[vtermanis]

When using the C extension (use_pure = False), query argument preparation results in reference leaks (via MySQL_convert_to_mysql) for the following argument types:

• Python 3: All int and float arguments, via PyObject_Str
• Python 2: All long arguments (i.e. whenever repr() thereof ends with an "L"), via PyObject_Repr (when numeric is not added to tuple)

Note: There are additional shortcomings in said function which are not addressed by this patch:

• Multiple API calls are not checked for failure/exception, for example:
  • PyTuple_New
  • PyObject_Str
  • PyObject_Repr
  • PyString_FromStringAndSize
• Potentially unnecessary string resize (Python 2 only) - can't it just be created one byte shorter?

[mysql-oca-bot]

Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment:
"I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it."
Thanks

[vtermanis]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=90861 for updates.
Thanks