Newly created gen_py modules sometimes fail to import in Python 3

[SReicheltPTV]

When accessing a COM server using gen_py modules on demand, some modules randomly fail to import after they have been generated. This is highly machine-dependent; on most computers the problem does not manifest itself at all, but on some it is quite reproduceable, using e.g.

import sys, win32com.client
c = <some on-demand static dispatch COM object>
m = sys.modules[sys.modules[c.__module__].__package__]
for clsid in m.CLSIDToPackageMap:
    win32com.client.gencache.GetModuleForCLSID(clsid)

On some machines, this will throw a "module not found" exception after about 10 iterations.

The cause of the problem seems to be a breaking change in Python 3.3, which is documented at https://docs.python.org/3/library/importlib.html#importlib.import_module. Specifically, it is now necessary to call importlib.invalidate_caches before importing the newly generated module. I will attach a PR.