bug in simplification

[Fergus Henderson]

Hi Simon,

I just added a test case tests/valid/simplify_bug.m which breaks the
current compiler.

The problem is that if compiling with `-O-1', we only do one pass of
simplification, and the "do once" thing in simplify.m to insert
commits around model_non goals in model_det conjunctions -- which is
normally done in the second pass -- never gets done.
As a result, invalid input is passed to the code generator, which aborts.

Simon, can you please fix this?

(The simplest way may be to just drop the attempt to do that
bit only once, and instead do it every time.)

-- 
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.