repeating the substitution.

Why didn't we think of this before?!

some of the security methods.

1. Some browsers don't understand attribute values in single quotes,
   so always use double quotes.

2. An undefined variable was referenced in the error reporting code in
   parseSubstitution().  (The error reporting cannot be reached unless
   _subst_re is changed -- but it is still a bug. :-)

the tracker.

mode opcodes.

Fix check_code_short_endtags(), which should have used <img /> since
the previous batch of changes.

- that the TALcode version of the macro is the same as that of the
  main program;

- that the mode (html or xml) of the macro is the same as that of the
  main program.

If either of these tests fails, raise METALError().

Added three new inquiries for TALcode programs: isCurrentVersion(),
getProgramVersion(), and getProgramMode().

generating HTML, and "/>" for XML, instead of always using "/>".

This is necessary for proper XHTML generation.