[TWAIN] Support of tl-x, tl-y, br-x, br-y
Options tl-x
, tl-y
, br-x
, br-y
still have to be implemented for TWAIN scanners.
TWAIN defines the scan frame as a single option: 'frames' with type TWTY_FRAME. So those options will have to be emulated using this single option, directly in TWAIN support.