dd API query dr_bbs_cross_ctis()

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on March 27, 2011 10:32:12_

actions like function replacing are simpler and more efficient when they
can assume that a callee will always be at the start of a bb.
if elision and indcall2direct options are off this assumption is valid.
we should add an API routine to query whether that's the case.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=427_