Switch to single intervals for FSF notices,
and consistently put them first.
Update copyright notices for 2024.
* cfg.mk (update-copyright-env): Use UPDATE_COPYRIGHT_FORCE=1,
UPDATE_COPYRIGHT_USE_INTERVALS=2.
* patch.man: Always use \(co, so that update-copyright
updates these dates.
* src/version.c: Correct Larry Wall copyright years.
Diffs can be indented by a variable number of spaces, tabs, or X characters.
Make sure that intuit_diff_type() only accepts context diffs where the first
and second line are indented identically, or else another_hunk() will fail.
* src/pch.c (intuit_diff_type): Remember the indentation of the last line. Only
recognize context diff hunks with the same amount of indentation on the first
and second line.
* tests/garbage: New test case.
* tests/Makefile.am (TESTS): Add test case.
