- version-neutral syntax for print and exec
- version-neutral exception handling: use exc_info()
- version-neutral exception raising: use raise A("x"), not A, "x"
- use e.args[0] instead of e[0]
- use urllib.request if urllib2 unavailable
- use http.client if httplib not available
- use socketserver if SocketServer not available
- use test.support if test_support not available

greentest/helper.py: try test.support if test_support is not available (py3k). Patch by Damien Churchill.

test_ssl.py: use urllib.request/parse instead of urllib2/urlparse; use http.server instead of HTTPServer

test__greenness.py: on py3k use urllib.request instead of urllib2 and http.server instead of BaseHTTPServer

- define basestring in hub.py for version that don't have it
- use exc_info()
- define exc_clear() in hub.py as no-op
- use "exec (xxx)" instead of "exec xxx"

- if we patch socket and getaddrinfo, create_connection becomes green too
- its interface is different from version to version

dnshelper.c: use PyImport_ImportModule instead of PyImport_InmportModuleNoBlock, the latter is not available in Python2.5

Hub: add new NOT_ERROR attribute equal to (GreenletExit, ) that lists the exceptions that do not require printing a traceback

Hub.handle_error: immediatelly raise error instead of scheduling it to be raised later if called in MAIN greenlet