Zexy fixes

Fixes the fallout from updating zexy to the latest IEM version, as reported on the mailing list. In particular:

• changed zexy/Makefile to build individual objects again, rather than a library
• backported rev. e294b129, 5e9124e9, 3cf58d70, as well as the hexmunger stuff (rev. 99e673e0 etc.) from the old version
• regenerated setup (Makefile and src/z_zexy.c) using src/makesource.sh

As far as I can tell, this fixes all reported issues.