When constructing an address range to "step" or "next" through,

find the largest address range (possibly combining multiple 
LineEntry's for this line number) that is contiguous.

This allows lldb's fast-step stepping algorithm to potentially
run for a longer address range than if we have to stop at every
LineEntry indicating a subexpression in the source line.

http://reviews.llvm.org/D15407
<rdar://problem/23270882> 

llvm-svn: 255590