[TxMt] Bug: Python bundle - constant_placeholder definition does not handle '%%'

[Andrew Durdin]

The 'constant_placeholder' definition incorrectly matches the '%s' in
a literal string '%%s' and highlights it; it should match the '%%'.

Fix: in the constant_placeholder definition, change:

    match = '%(\([a-zA-Z_]+\))?(0|\-|\+)?([0-9\.]*)?[diuoxXfeEgGsrc]';

to:

    match = '%(\([a-zA-Z_]+\))?(0|\-|\+)?([0-9\.]*)?[diuoxXfeEgGsrc%]';