For later use in IFindFilter.

Reviewed-by: ck

 - lessens open file handles
 - improves help plugin startup further

Task-number: QTCREATORBUG-337
Reviewed-by: ck

Reviewed-by: ck

Reviewed-by: ck

Make the check more generic, to also work for all other Qt namespaces
than qt.ver.s.ion. Still there's something broken in Qt webkit or so.

Reviewed-by: ck

Reviewed-by: kh

Both implementations are now split into two source files, based on the
base class type. They share also a commen implementation, but the class
interface looks now clean to the outside. Adopt other classes for use.