…_xxOR.rst

The rationale for this change is as follows:

re.escape() is only used to cache single Unicode characters
in shell patterns; we may heuristically assume that they are
ISO-8859-1 encodable, thereby requiring a cache of size 256.
To allow non-traditional glyphs (or alphabets with a small
number of common glyphs), we double the cache size.

Co-authored-by: Barney Gale <[email protected]>