We should not use the date in the header when patching, because that

can lead to newly-patched files having an older date than generated
files.  I also got rid of the date-portion of the diff header and I
changed the dir prefixes to be "old/" and "new/" (we now require
"patch -p1").  Also dumped the setting of $ENV{TZ} to 'UTC' and made
a few code optimizations.