Power PPC 128bit modulo and carry instruction fix

Power PPC 128bit modulo and carry instruction fix

VEX commit 3209 fixed: an issue with caculating the carry to the next 32-bit
chunk for the Power PPC 128-bit add and subract instructions: vaddcuq, vadduqm,
vsubcuq, vsubuqm, vaddecuq, vaddeuqm, vsubecuq, vsubeuqm

The corresponding test case didn't catch the issue.  The valgrind commit
15790 adds data values to the test that verify the issue is fixed.

This commit is to update the NEWS file.

Valgrind Bugzilla 359472

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15796