Fix assorted minor bogosity in GSSAPI transport error messages.

Fix assorted minor bogosity in GSSAPI transport error messages.

I noted that some buildfarm members were complaining about %ld being
used to format values that are (probably) declared size_t.  Use %zu
instead, and insert a cast just in case some versions of the GSSAPI
API declare the length field differently.  While at it, clean up
gratuitous differences in wording of equivalent messages, show
the complained-of length in all relevant messages not just some,
include trailing newline where needed, adjust random deviations
from project-standard code layout and message style, etc.