Apply xcode fixes from Jan Weiß, except one chunk that seems mistaken.
merge
Apply last chunk of Jan's xcode patches.
I misread, it is needed after all.
Add support for setting extra fields, untested.
Fix for newly added files and for files without extra fields.
Document that flags have to be passed.
Handle NULL file names. From Roland Ortloff.
Consistently check for _stricmp
Remove checks for obsolete (since VC 2005) _strcmpi.
Clean up.
Add Roland Ortloff <Ortloff.R@gmx.de>.
Add zip_archive_set_tempdir to specify directory to use for temp file while closing.
(NULL to place it in the same directory as the original file.)

This is needed to use libzip in OS X sandboxed applications.  It's
a temporary hack that will be solved properly once we have an I/O
abstraction layer.
Fix typo.