<rdar://problem/13315663>

commands of the form 
frame variable -f c-string foo
where foo is an arbitrary pointer (e.g. void*) now do the right thing, i.e. they deref the pointer and try to get a c-string at the pointed address instead of dumping the pointer bytes as a string. the old behavior is used as a fallback if things don’t go well

llvm-svn: 177799