Add various bound checks

Add various bound checks

Add bounds checks where Coverity otherwise reports a defect.  Most of
these checks are unlikely to be triggered in practice (Unicode regexps
are unused, and the caller of gss_krb5int_make_seal_token_v3 won't
have a plaintext object larger than half of the address space).  The
checks in dump.c could prevent memory access errors resulting from a
malformed dump file.

[ghudson@mit.edu: rewrote commit message]

ticket: 8578 (new)