mark conditional branches and string loops as predicated

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on October 30, 2014 18:52:04_

The new predication API (xref issue #269 , issue #1181 ) should probably consider general
conditional branches to also be predicated. For x86, OP_jcc is simple to
translate to DR_PRED_ constants -- but we'd have to add new ones or ensure
DR_PRED_COMPLEX's assumptions hold for OP_jecxz.

What about OP_rep_movs for when ecx is 0?

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1556_

Start by reading the predication API and the existing x86 translation for OP_jcc, then compare the assumptions behind DR_PRED_COMPLEX with OP_jecxz and OP_rep_movs. The issue is complete only after the project decides which conditional branches and string-loop cases count as predicated and defines the required DR_PRED constants or semantics.

Written by the indexing model from the issue text.