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This commit replaces the readdir() loop with scandir. This means a well-
defined, reproducible sort order, with the downside that we will need to
store ALL directory entries in memory to sort them.

I am too lazy to add a switch to change how it is supposed to work. This
is only a proof-of-concept.

Co-Authored-By: Bernhard M. Wiedemann <bwiedemann suse.de>

with SOURCE_DATE_EPOCH
to allow for reproducible builds of .zip files

See https://reproducible-builds.org/ for why this is good
and https://reproducible-builds.org/specs/source-date-epoch/
for the definition of this variable.

Uses clamping to keep older mtimes than SOURCE_DATE_EPOCH intact.

and drop the obsolete --no-extra commented code

Without this patch, memory leaks occur when using zip-3.0
to append files to an existing archive file.

https://bugzilla.suse.com/show_bug.cgi?id=1068346

by in2ex/ex2in's chopping off path prefixes.

Do not record build time in executable to have reproduceable builds