#75 Require wact: prefix for compile time attributes

[Harry Fuecks]

Following discussions in these two threads;

http://sourceforge.net/mailarchive/forum.php?thread_id=5059804&forum_id=35579
http://sourceforge.net/mailarchive/forum.php?thread_id=5065185&forum_id=35579

The basic problem was someone using a core:include like;

<core:include file="{$Filename}">

Then attempting to set $Filename at runtime.

Think it might help reduce confusion to prepend
attributes which only have a meaning at compile time
with a wact: prefix i.e.

<core:include wact:file="{$Filename}">

That way it will be easy to document which attributes
cannot be altered at runtime. We could also check, in
the compiler, and raise a relavent error message when
we see an attribute named wact:something and that it
has no compile time value (via core:set / core:import).

See also feature request 911003:
http://sourceforge.net/tracker/index.php?func=detail&aid=911003&group_id=85372&atid=575987