Bug#553500: blank window workaround patch works only by accident

[Monty Montgomery]

Hi folks,

I have a new 'release' of gPlanarity with a few new translations, and
a correct fix to the blank window bug.  See:
http://web.mit.edu/~xiphmont/Public/gPlanarity.html

The fix for this bug suggested in this bug report (553500) is not
correct and works by accident, meaning it could also break at any
time.

The bug is caused by a restriction/clarification in the GDK/Cairo
interaction API where a cairo target created for a given GDK window is
now only gauranteed to be valid for the span of a single GDK event.
gPlanarity had previously been caching a single cairo_t upon
allocation of the window and attempting to use it for all following
drawing operations.  It now allocates a cairo_t for the GDK window on
demand for each drawing op, then discards it.  That is the correct fix
to the bug.

Cheers!
Monty