ui: add new config option for help text width
Before this patch, when printing help text using `hg help`, or `hg log -h`,
the output will wrap at 78 chars even if the user has a bigger terminal width
and there is no config option to change it, making the experience different
from the commonly used `man` tool.
This patch introduces a new config option `ui.textwidth`, which replaces the
hardcoded number. It's set to 78 by default to maintain compatibility. When
set to 0, `hg help` will behave more like `man`.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.