git-add: add ignored files when asked explicitly.

git-add: add ignored files when asked explicitly.

One thing many people found confusing about git-add was that a
file whose name matches an ignored pattern could not be added to
the index.  With this, such a file can be added by explicitly
spelling its name to git-add.

Fileglobs and recursive behaviour do not add ignored files to
the index.  That is, if a pattern '*.o' is in .gitignore, and
two files foo.o, bar/baz.o are in the working tree:

    $ git add foo.o
    $ git add '*.o'
    $ git add bar

Only the first form adds foo.o to the index.

Signed-off-by: Junio C Hamano <junkio@cox.net>