Add more assertions to catch accesses outside of

Add more assertions to catch accesses outside of
arrays.  Also, as a convenience, don't barf, just
return false, if someone calls isTruncStoreLegal
or isLoadXLegal with an extended type for the in
memory type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46352 91177308-0d34-0410-b5e6-96231b3b80d8