Problem:    Crash when there is an error in a timer callback. (Aron Griffis,
            Ozaki Kiichi)
Solution:   Check did_throw before discarding an exception.  NULLify
            current_exception when no longer valid.

Problem:    Using number for exception type lacks type checking.
Solution:   Use an enum.

Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.

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

Problem:    Should_free flag set to FALSE.
Solution:   Set it to TRUE. (Neovim 4415)

Problem:    Crash when evaluating the pattern of ":catch" causes an error.
            (Dominique Pelle)
Solution:   Block error messages at this point.

Problem:    Using old style function declarations.
Solution:   Change to new style function declarations. (script by Hirohito
            Higashi)

Problem:    Still using __ARGS.
Solution:   Remove __ARGS in several files. (script by Hirohito Higashi)

Problem:    Python: When vim.eval() encounters a Vim error, a try/catch in the
            Python code doesn't catch it. (Yggdroot Chen)
Solution:   Throw exceptions on errors in vim.eval(). (ZyX)

Problem:    New regexp engine: Matching plain text could be faster.
Solution:   Detect a plain text match and handle it specifically.  Add
            vim_regfree().