[PyQt] SIP suggestion: warnings for /Transfer/ with /Supertype=sip.simplewrapper/

[Kevin Watters]

I updated to a newish SIP snapshot and was playing around with using 
/Supertype=sip.simplewrapper/ when possible.

The note in the docs about simplewrapper objects being unable to take 
part in ownership transfer is good, but it might be even more useful for 
SIP to warn or fail when you have a sip.simplewrapper type participating 
in /Transfer/--since at runtime, it just silently remains owned by 
Python. Most of my libraries' transfer cases were covered by one common 
base class, which got /Supertype=sip.wrapper/ -- but there were a few 
classes that weren't covered by this, and they were a (minor) pain to 
hunt down.

Just a suggestion!

- Kevin