Fix com_err.h dependencies in gss-kernel-lib

Fix com_err.h dependencies in gss-kernel-lib

make check was failing in util/gss-kernel-lib due to dependencies
when the build is configured with --with-system-et, because depfix.pl
wasn't smart enough to substitute the dependency on com_err.h in the
current directory.  Make depfix.pl smarter, and adjust COM_ERR_DEPS
to be com_err.h in gss-kernel-lib when building with the bundled
com_err.

ticket: 7014
target_version: 1.10
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25468 dc483132-0cff-0310-8789-dd5450dbe970