GUI specific paste functions for X11 and WIN32 in paste_handler() moved to
the new function
- get_clipboard_text() prepared for other GUIs
- set_clipboard_text() has now a return value (0 = failed or not implemented)
- use portable code in copy_handler() if set_clipboard_text() fails
- snapshot_handler() prepared for adding a file dialog call
- writing snapshot file in binary mode (LF->CRLF conversion already done)
GUI specific copy functions for X11 and WIN32 in copy_handler() moved to
the new function
- set_clipboard_text() prepared for other GUIs
- value of text mode cursor variables fixed (and renamed in x.cc)
- BX_ERROR message in snapshot_handler() fixed
