gdkAtomIntern(atom.name, only.if.exists = FALSE)
atom.name
only.if.exists
TRUE
, GDK is allowed to not create a new atom, but
just return GDK_NONE
if the requested atom doesn't already
exists. Currently, the flag is ignored, since checking the
existance of an atom is as expensive as creating it.GdkAtom
] the atom corresponding to atom.name
.