Problem: 'wildmenu' only shows few matches.
Solution: Add the "pum" option: use a popup menu to show the matches.
(Yegappan Lakshmanan et al., closes#9707)
Problem: Loop for handling keys for the command line is too long.
Solution: Move wild menu handling to separate functions. (Yegappan
Lakshmanan, closes#6856)
Problem: Crash in command line expansion when out of memory.
Solution: Check for NULL pointer. Also make ExpandGeneric() static.
(Dominique Pelle, closes#5437)
