Move some infra bits of lib/krb5/ to lib/base/ (1)

Move some infra bits of lib/krb5/ to lib/base/ (1)

This is the first of two commits in a series that must be picked
together.

This series of two commits moves parts of lib/krb5/ infrastructure
functionality to lib/base/, leaving behind wrappers.

This commit only renames files to enable git log/diff/blame to follow
the renames: to help future code archeology, and to make reviewing these
two commits easier.

The next commit in this series ensures that the moved files have the
correct content (i.e., defining heim APIs instead of krb5 APIs), and
will create files in lib/krb5 with the same names and krb5 API wrappers
around the new heim API functions.

The next commit also explains the motivation, which, briefly, is to:

 - remove krb5 API usage from lib/gssapi/,
 - enable the use of configuration and plugins in lib/hx509/
   (as well as lib/gssapi/ and future projects),

and

 - enable the further disentanglement of bx509d from kdc/.