Use new error message wrapping APIs

Use new error message wrapping APIs

Define internal names k5_prendmsg and k5_wrapmsg and use them where we
amend error messages.  This slightly changes the error message when we
fail to construct FAST AP-REQ armor, decrypt a FAST reply, or store
credentials in a gic_opts output ccache.  Adjust the test suite for
the latter of those changes.

[ghudson@mit.edu: define and use internal names for brevity; pull in
test fix from later commit; expand commit message; fix redundant
separators in LDAP messages]

ticket: 8046