be answered with the comments removed.
There are many places that require checks when doing arithmetic for memory
sizes when allocating memory. Otherwise, overflow is possible with
a subsequent crash.
Fix SF #1777057 which was a result of not initializing the new BufferError
properly. Had to update the test for exceptions for BufferError too.
This uses up to 12.5% overallocation, not entirely unlike list_resize().
Could probably use more tweaks for odd allocation patterns, TBD.
Also add __alloc__() method which returns the actually allocated size.
PS. I'm now convinced that we need something like "".join(); later.