Homogenized existence of "hasXYZ" methods, removed where necessary.

"hasXYZ" methods now exist for every attribute except for optional attributes with the simple pattern "getter:attribute(), setter:attribute(...), deleter:attribute(none_t t)". For those "hasXYZ" has been removed where existing, since "attribute()" can be used instead.
Merge pull request #159 from balint42/fix_hasXYZ

Fix existence of hasXYZ methods
checking only the last commit makes it much easier :)