Allow proper dumping of inttoptr.

ICE doesn't really need to deal with inttoptr, doesn't (yet) support
lowering, and in fact wants an assignment instruction in this case.
But it's good to be able to dump this if we're trying to compare
output against input for equivalence.
If -notranslate is used, don't change inttoptr into an assignment.

This is useful for testing dump output against the input.
Fix the way "@" is prepended to globals for dumping.
Fix tests to be more amenable to high-level testing.

Checks for "call foo" are changed to "call @foo".

Most of the other changes wouldn't have been necessary if the .ll
files were proper PNaCl bitcode.