* Expand the "-s" flag to -s {srcdir|tgzfile|tempdir}.
* Deprecate the "-b" flag. It is replaced by "-s tempdir".
* Change "-s srcdir" to refer to the top of the source tree (e.g.
/usr/src) instead of the etc subdirectory.
In etcupdate's interactive phase, enhance the "s" command to be able
to invoke alternative diff commands.
Also some style changes.
Approved by christos
7e321ef839