Rename db2 header files db.h and db-config.h in the source tree, so

Rename db2 header files db.h and db-config.h in the source tree, so
that there will always be only one version of each name in the include
path (namely, the copy made in the build tree, or the generated db.h
if not using the in-tree one).  This should fix some minor problems
with different dependency lists generated on different systems.

Sort and uniquify dependency header names before doing substitutions,
as well as after.  Look for the db2 headers listed in sorted order.

Don't copy db-ndbm.h into the build tree; let libdb2 find it from the
source tree only.

Update dependencies.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22572 dc483132-0cff-0310-8789-dd5450dbe970