Save compatibility

Fixes the save incompatibility from https://github.com/CleverRaven/Cataclysm-DDA/pull/8678#issuecomment-53203563 - 2147483648 is a nice power of two, but the save from #8593 does not contain it, it contains 2147483647.

Fixes #8503 - convert bionic power from old save files to new power scale. ~~Simply added a boolean entry to the json data (alternatively the savegame version could be increased, but I'm not sure what side effects that has). The value of the marker defaults to false when it's not present (old save), it's set to true for all new saves.~~ Edit: see comment.