Modified ObjectFile::SetLoadAddress() to now be:

ObjectFile::SetLoadAddress (Target &target,
                            lldb::addr_t value,
                            bool value_is_offset);

Now "value" is a slide if "value_is_offset" is true, and "value" is an image base address otherwise. All previous usage of this API was using slides.

Updated the ObjectFileELF and ObjectFileMachO SetLoadAddress methods to do the right thing.

Also updated the ObjectFileMachO::SetLoadAddress() function to not load __LINKEDIT when it isn't needed and to only load sections that belong to the executable object file.