Fix thinko in subproject entry sorting

Fix thinko in subproject entry sorting

This fixes a total thinko in my original series: subprojects do *not* sort
like directories, because the index is sorted purely by full pathname, and
since a subproject shows up in the index as a normal NUL-terminated
string, it never has the issues with sorting with the '/' at the end.

So if you have a subproject "proj" and a file "proj.c", the subproject
sorts alphabetically before the file in the index (and must thus also sort
that way in a tree object, since trees sort as the index).

In contrast, it you have two files "proj/file" and "proj.c", the "proj.c"
will sort alphabetically before "proj/file" in the index. The index
itself, of course, does not actually contain an entry "proj/", but in the
*tree* that gets written out, the tree entry "proj" will sort after the
file entry "proj.c", which is the only real magic sorting rule.

In other words: the magic sorting rule only affects tree entries, and
*only* affects tree entries that point to other trees (ie are of the type
S_IFDIR).

Anyway, that thinko just means that we should remove the special case to
make S_ISDIRLNK entries sort like S_ISDIR entries. They don't.  They sort
like normal files.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>