format-python-brace: Support chained expression
* gettext-tools/src/format-python-brace.c (parse_directive): Recognize
chained getattr/getitem expressions.
* gettext-tools/tests/format-python-brace-1: Add test for the case where
both getattr and getitem are used.
Reported by Paul Franklin in:
https://lists.gnu.org/archive/html/bug-gettext/2016-03/msg00017.html
