Problem:    balloon_show() only works in terminal when compiled with the GUI.
Solution:   Add FEAT_BEVAL_GUI and refactor to move common code out of the GUI
            specific file.

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

Problem:    Using "u_char" intead of "char_u", which doesn't work everywhere.
            (Jörg Plate)
Solution:   Use "char_u" always.

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

Problem:    EINTR is not always defined.
Solution:   Include errno.h in vim.h.

A few minor changes.