[PyQt] Private sip modules conflict with public sip module

[Scott Talbert]

Hi,

See the below example:

$ python3
Python 3.7.4 (default, Jul  9 2019, 16:32:37)
[GCC 9.1.1 20190503 (Red Hat 9.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import PyQt5.sip
>>> import sip
>>> sip
<module 'PyQt5.sip' from 
'/usr/lib64/python3.7/site-packages/PyQt5/sip.so'>
>>>

Basically, if you import a private sip module and then import the public 
one, it doesn't work.  It seems to be due to this:

https://www.riverbankcomputing.com/hg/sip/file/4.19-maint/siplib/siplib.c#l1293

Scott