pretty: expand tabs in indented logs to make things line up properly
A commit log message sometimes tries to line things up using tabs,
assuming fixed-width font with the standard 8-place tab settings.
Viewing such a commit however does not work well in "git log", as
we indent the lines by prefixing 4 spaces in front of them.
This should all line up:
Column 1 Column 2
-------- --------
A B
ABCD EFGH
SPACES Instead of Tabs
Even with multi-byte UTF8 characters:
Column 1 Column 2
-------- --------
Ä B
åäö 100
A Møøse once bit my sister..
Tab-expand the lines in "git log --expand-tabs" output before
prefixing 4 spaces.
This is based on the patch by Linus Torvalds, but at this step, we
require an explicit command line option to enable the behaviour.