Problem: Completion of user defined functions is not covered by tests.
Solution: Add tests. Also test various errors of user-defined commands.
(Dominique Pelle, closes#1413)
Problem: The short form of ":noswapfile" is ":noswap" instead of ":now".
(Kent Sibilev)
Solution: Only require three characters. Add a test for the short forms.
Problem: When there is an CmdUndefined autocmd then the error for a missing
command is E464 instead of E492. (Manuel Ortega)
Solution: Don't let the pointer be NULL.
