poppler: share most things between glib and qt4 versions

Most of the stuff was duplicated (headers, the core library).
The new solution makes the _qt4 package use the _glib one,
because it depended on glib through cairo anyway
(and _glib bindings themselves are just ~350kB).

This also fixes a problem that mergeAttrsByFuncDefaultsClean
didn't merge patches, which affected dbus.libs.