when eliding in bbs, pass both sides separately to client and merge afterward

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on May 04, 2012 16:58:38_

split from issue #198 this was PR 214169

1) We call the client's bb hook twice, once for 1st bb and again for target
of call*. Client is not allowed to change the call itself. We then
merge the two.

Upside: client sees original instrs
Downside: more complex and less efficient for us to generate 2 separate
app ilists and then merge them. Also, client can't change the control flow.

We could extend this to all elisions.

For now, we're turning off elision by default for -code_api

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=770_