Problem: No simple way to label quickfix entries.
Solution: Add the "module" item, to be used instead of the file name for
display purposes. (Martin Szamotulski, closes#1757)
Problem: Need several lines to verify a command produces an error.
Solution: Add assert_fails(). (suggested by Nikolay Pavlov)
Make the quickfix alloc test actually work.
Problem: Alloc_id depends on numbers, may use the same one twice. It's not
clear from the number what it's for.
Solution: Use an enum. Add a function to lookup the enum value from the
name.
