Refine CFG so that '&&' and '||' don't lead to extra confluence points when used in a branch, but

instead push the terminator for the branch down into the basic blocks of the subexpressions of '&&' and '||'
respectively.  This eliminates some artifical control-flow from the CFG and results in a more
compact CFG.

Note that this patch only alters the branches 'while', 'if' and 'for'.  This was complex enough for
one patch.  The remaining branches (e.g., do...while) can be handled in a separate patch, but they
weren't immediately tackled because they were less important.

It is possible that this patch introduces some subtle bugs, particularly w.r.t. to destructor placement.
I've tried to audit these changes, but it is also known that the destructor logic needs some refinement
in the area of '||' and '&&' regardless (i.e., their are known bugs).

llvm-svn: 160218