Adds 16 and 32 bit fnsave/frstor, and 0x66 prefix on fldl, to guest

Adds 16 and 32 bit fnsave/frstor, and 0x66 prefix on fldl, to guest
amd64.

The Oracle/Sun HotSpot Java virtual machine uses fnsave and frstor,
which valgrind supports for x86 but not amd64. Even more interesting,
HotSpot uses the 0x66 size prefix on these instructions, and on
fldl. This patch adds the 16- and 32-bit versions of fnsave/frstor to
the amd64 guest, and tolerates the 0x66 size prefix on fldl (but only
on these three fpu instructions, even though the AMD docs say all
other fpu instructions (except fnstenv and fldenv) *ignore* 0x66).

Fixes #294191.  (Eliot Moss, moss@cs.umass.edu)

git-svn-id: svn://svn.valgrind.org/vex/trunk@2253