This patch improves handling of the Z bit in the status register in a 
variety of ways to improve either the code size or code speed on various 
H8 subtargets.

For example, we can test the zero/nonzero status of the upper byte of a 
16 bit register using mov.b, we can move the Z or an inverted Z into a 
QImode register profitably on some subtargets. We can move Z or an 
inverted Z into the sign bit on the H8/SX profitably, etc.

I've actually had this patch in my tester for over a year, but got crazy 
busy and hadn't bothered to upstream it until now. Naturally it has been 
working all that time without regressions.

Pushed to the trunk.


Jeff