Small documentation update regarding debugging aids: - doc/debugging.txt: removed HYPERDBDEBUG and HYPERDBTRACE and replaced it with the text for SENDMAILDEBUG from doc/developers.txt. A short code inspection showed that to be correct. - refered to debugging.txt from developers.txt to have one unique place for documenting debugging aids. - Clarified for SENDMAILDEBUG that no email will be send if it is set.

# In Python 3 the "anydbm" module was renamed to be "dbm" which is now a
# package containing the various implementations. The "wichdb" module's
# whichdb() function was moved to the new "dbm" module.

try:
    # old school first because <3 had a "dbm" module too...
    import anydbm
    from whichdb import whichdb
except ImportError:
    # python 3+
    import dbm as anydbm
    whichdb = anydbm.whichdb