diff: extras/trailed_update enhancements + bug fixes

[Fergus Henderson]

Various bug fixes and enhancements to var.m and other stuff in
extras/trailed_update.

extras/trailed_update/var.m:
	Add code to detect floundering.
	Change the code for debug_freeze/3 to avoid a floundering warning.
	Add new predicates debug_freeze/4 (to go with debug_freeze/3)
	and dump_var/3.
	Fix a bug in freeze/3 (higher-order terms are monomorphic, so
	there is no need to explicitly pass type-infos when calling them).
	Fix a bug in wakeup_delayed_goals/2 (we need to set the binding
	to ground _before_ waking up the goals).

extras/trailed_update/Mmakefile:
	Add `ML = ml --mercury-libs shared', so that it will work on Linux.

extras/trailed_update/samples/Mmakefile:
	Make it work with shared libraries on Linux.

extras/trailed_update/tr_store.m:
	Add a prototype for ML_compare_typeinfo().

extras/trailed_update/unsafe.m:
	Change the C code for unsafe_perform_io to match the new
	interface for exported Mercury procedures that do I/O --
	there is no longer any need to pass dummy io__state arguments
	in the C code.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3         |     -- the last words of T. S. Garp.