Allow other targets

For example, (F)CKEditor allows these link targets:

-
- : user may specify the name of target frame
-
: user may specify the name of the popup window and other properties (width, height, left pos, top pos, etc...)
New Window (_blank)
Topmost Window (_top)
Same Window (_self)
Parent Window (_parent)

Currently, the module supports _blank and _top only.