Problem:    No test for 'termwinkey'.
Solution:   Add a test.  Make feedkeys() handle terminal_loop() returning
            before characters are consumed.

Problem:    Cannot use 'balloonexpr' in a terminal.
Solution:   Add 'balloonevalterm' and add code to handle mouse movements in a
            terminal. Initial implementation for Unix with GUI.

Problem:    Mac features are confusing.
Solution:   Make feature names more consistent, add "osxdarwin". Rename
            feature flags, cleanup Mac code. (Kazunobu Kuriyama, closes #2178)

Problem:    Recorded key sequences may become invalid.
Solution:   Add back KE_SNIFF removed in 7.4.1433. Use fixed numbers for the
            key_extra enum.

Problem:    Recognizing urxvt mouse codes does not work well.
Solution:   Recognize "Esc[*M" and "Esc[*m". (Maurice Bos, closes #1486)

Problem:    The buffer used to store a key name theoreticaly could be too
            small. (Coverity)
Solution:   Count all possible modifier characters.  Add a check for the
            length just in case.

Problem:    Vim does not support bracketed paste, as implemented by xterm and
            other terminals.
Solution:   Add t_BE, t_BD, t_PS and t_PE.

Problem:    Modelines in source code are inconsistant.
Solution:   Use the same line in most files.  Add 'noet'.  (Naruhiko Nishino)

Problem:    The Sniff interface is no longer useful, the tool has not been
            available for may years.
Solution:   Delete the Sniff interface and related code.

Problem:    Cannot select beyond 222 columns with the mouse in xterm.
Solution:   Add support for SGR mouse tracking. (Hayaki Saito)