In preparation for generating method signatures for the manual.
This change gets rid of bogus false|null return types, a few unnecessary trailing backslashes, and settles on using ? when possible for nullable types.
Instead of false. This is consistent with how other methods like
SplFileInfo::getPath() behave. It's also a requirement before
SplFileInfo::__toString() calls SplFileInfo::getPathname() and
needs to return a string.
