Make KDC "status" statements more homogeneous

Generally we want KDC status strings to be concise, informative and follow
some common rules:

- All letters in the status string should be capitalized;
- the words in the status phrase are separated by underscore;
- abbreviations should be avoided.  Some acceptable "standard" acronyms
  are AS_REQ, TGS_REP etc.
- since in almost all cases KDC status is set on error, no need
  to state this fact as part of the status string;
- KDC status string should be an imperative phrase.

For example, "DECRYPT_SERVER_KEY".

This commit is to modify some KDC status messages to follow this format.

Even though KDC status messages are not standardized, it is possible that some
administrators use them in the Kerberos log file processing. Hence, the vast
majority of them are left unchanged pending further investigation (mostly,
feedback from the administrators).
Document 1.12 changes in MIT Kerberos Features doc

ticket: 7857
Use TAILQ macros instead of CIRCLEQ in libdb2

The optimizer in gcc 4.8.1 (but not the current gcc head revision)
breaks the queue.h CIRCLEQ macros, apparently due to an overzealous
strict aliasing deduction.  Use TAILQ macros in the libdb2 mpool code
instead.

ticket: 7860
Use system dictionary for db2 tests again

The built-in word list is not long enough for all of the libdb2 tests
to run properly.  Revert d21a86e47a7cda29225013e08d060095b94b2ee7 and
go back to using the system dictionary if we find one.  However, omit
any lines from the chosen word list which contain non-alphabetical
characters.

ticket: 7860