Test for large Zip archives, following code for large Tar test.
Fix several bugs:
 * comparison function for ordering entries in reader was wrong
 * writer wasn't including 64-bit sizes for entries of exactly 0xffffffff bytes
Also, add options to suppress CRC calculations and checks
(otherwise, this test spends a *lot* of time in CRC routines).
Parse out the extra data before trying to insert into the tree.

Since the tree is organized by offset, we
need the full offset from the extra data
(in the case of 64-bit offsets) before we do the
insertion.

While here, fix an obvious blooper: initialize the CRC function.
Expand the large zip test a bit
Extend large zip test to cover streaming reader as well.
Update some comments
Skip stored data quickly when size is known at beginning even when CRC is at end
Return uncompressed size if it's known, even if compressed size and/or CRC are deferred.
Fix large zip test in streaming mode.
Make zip->offset tracking more consistent.
Eliminate zip reader's redundant tracking of file position (the archive already does this).