Merge in branches/DCAS:

Merge in branches/DCAS:

This branch adds proper support for atomic instructions, proper in the
sense that the atomicity is preserved through the compilation
pipeline, and thus in the instrumented code.

The change adds a new IR statement kind, IRStmt_CAS, which represents
single- and doubleword compare-and-swap.  This is used as the basis
for the translation of all LOCK-prefixed instructions on x86 and
amd64.

The change also extends IRExpr_Load and IRStmt_Store so that
load-linked and store-conditional operations can be represented.  This
facilitates correct translation of l[wd]arx and st[wd]cx. on ppc in
the sense that these instructions will now eventually be regenerated
at the end of the compilation pipeline.

git-svn-id: svn://svn.valgrind.org/vex/trunk@1901