Simplified check for libcurl 7.19.1

Simplified check for libcurl 7.19.1 or greater,
necessary for options CURLOPT_USERNAME,
CURLOPT_PROXYUSERNAME and CURLOPT_CERTINFO.
Safer define for Py_TYPE()

Define Py_TYPE() only for Python 2.6 or greater.
If it's not defined and Python version is correct
then something else is wrong.
Removed unnecessary check for Python 2.2 or older

Defining PY_LONG_LONG is not needed anymore since
pycurl already requires Python 2.4 or greater.
Removed defines for PY_SSIZE_T_MAX/MIN

Removed unnecessary defines for PY_SSIZE_T_MAX
and PY_SSIZE_T_MIN.
Merge pull request #62 from romuloceccon/cleanup_defines

Cleanup defines