Infrastructure cleanup part 2.
Replace Iex_Mux0X with Iex_ITE (if-then-else) 
and 
IRExpr_Mux0X( cond, iffalse, iftrue ) with
IRExpr_ITE  ( cond, iftrue, iffalse );


git-svn-id: svn://svn.valgrind.org/vex/trunk@2668 8f6e269a-dfd6-0310-a8e1-e2731360e62c