support TSX fallback pc control xfer

[derekbruening]

From bruen...@google.com on November 06, 2013 13:33:59

Intel's TSX adds transactional execution support. Of relevance to DR:
OP_xend, on failure to commit, sets eip to a fallback pc stored in
OP_xbegin (it's a Jz operand to OP_xbegin). This issue covers supporting
such a control transfer.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1314