Use two approaches for intercepts
Use two approaches for intercepts

 - the existing INT3/SIGTRAP approach is used if running under
   Valgrind, because it works and the the HLT instruction is
   not recognised by Valgrind.

 - a new HLT/SIGSEGV approach is used is running normally (where
   either approach works) or under gdb (where the SIGTRAP approach
   doesn't work because gdb is jealous of SIGTRAP).

This sucks a bit.  If SIGSEGV is generated in some other way, like a
bug, y'know, that we test for, then it's lost, which is BAD.  Plus the
expected SIGSEGVs are visible and confusing to the gdb user.  An
approach using no signals at all would be best.

greig-hamilton/novaprova,greig-hamilton/novaprova,novaprova/novaprova,novaprova/novaprova,greig-hamilton/novaprova,novaprova/novaprova,gnb/novaprova,loom-project/novaprova,gnb/novaprova,novaprova/novaprova,loom-project/novaprova,gnb/novaprova,loom-project/novaprova,greig-hamilton/novaprova,gnb/novaprova,loom-project/novaprova,gnb/novaprova,greig-hamilton/novaprova,novaprova/novaprova