Start refactoring Zip writer:
 * Build list of entries for Central directory at entry_finish
   (So we can switch in-memory Central dir to a list of binary blobs.)
 * Rename some variables to clarify the code.
 * Add 'zip64' option to force zip64 extensions for testing
Adjust format for longer test names.
Support Zip64 extra data fields for handling large entries.

Process extra data fields for central directory and local file headers
so we get correct full size information in both cases.
Correct central directory vs. local file header sanity check
to compare full size information (including data picked out of
the extra data).

Note:  This does not yet support the Zip64 end-of-central-directory
marker so doesn't correctly handle very large archives.
Refactor Zip writer.

Zip writer no longer preserves full archive_entry objects for
every entry; it just accumulates the actual bytes to be put
into the central directory.  Most of the central directory file
header is formatted at the same time as the local file header.
The header formatting is refactored to make it easier to support
variable-length extra data.

The tests are adjusted to match the new output:  We include more
detailed extra data in the central directory, we're more selective
about generating data descriptors (they're not needed for directory
entries, for instance), UT extra data now includes only the time
fields specified by the user, we're setting the "version required"
field more accurately.

There are some initial attempts to include Zip64 extensions
when appropriate; that still needs lots of work.  I'm not
yet sure how to test Zip64 support without generating gigantic
archives.  Hmmm...
Remove the redundant test.
Remove deleted test from makefiles
gitignore all emacs backup files
Remove unused variables