Drop instruction suffix for some unary x87 instructions; switch from 'force' to 'check' terminology; define a proper type for 32-bit x86 registers.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15250 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02