Change lldb.value.__int__() so that it takes into account the signedness of...

Change lldb.value.__int__() so that it takes into account the signedness of the value being cast to return a Python number with the proper value

The explicit APIs on SBValue obviously remain if one wants to be explicit in intent, or override this guess, but since __int__() has to pick one, an educated guess is definitely better than than always going to signed regardless

Fixes rdar://24556976

llvm-svn: 260349