Add an "offset" option to "break set -n" and "break set -f -l".

That way you can set offset breakpoints that will move as the function they are 
contained in moves (which address breakpoints can't do...)

I don't align the new address to instruction boundaries yet, so you have to get
this right yourself for now.

<rdar://problem/13365575>

llvm-svn: 263049