patch: make _addmodehdr a function under trydiff
addmodehdr is a header helper, same as diffline, so it doesn't
need to be a top-level function and can be nested under trydiff.
In upcoming patches we will generalize this approach for
all headers.
$ "$TESTDIR/hghave" pyflakes || exit 80
$ cd "`dirname "$TESTDIR"`"
$ pyflakes mercurial hgext 2>&1 | "$TESTDIR/filterpyflakes.py"
hgext/inotify/linux/__init__.py:*: 'from _inotify import *' used; unable to detect undefined names (glob)