add casArray# primop, similar to casMutVar# but for array elements
Tweak stg_casArrayzh as per Simon Marlow's suggestion.
Update stg_casArrayzh to conform to new CMM conventions.
Add PrimOp: casIntArray#.  Modify casMutVar# for 'ticketed' style.
Add PrimOp fetchAddIntArray# plus supporting C function atomic_inc_by.
Eliminate atomic_inc_by and instead medofiy atomic_inc.
minor bugfix to casIntArray# and fetchAddIntArray#
Merge branch 'master' into atomics
minor: remove tabs from file