Move GTK2 initialization into the kernel
Add some more ADVISORY possibilities
RMImport: Drop code made redundant by use of setdefault()
window: Abbreviate G->G->window-> as the names can be referenced directly
window: Standardize on the name closewindow rather than window_close.

Though it appears to be a pointless change, this removes one small barrier to
merging the movablewindow and window.pike code.