global: More fixes to mismatched bool vs int handling

auth: Mark memory pools as growing and use the same sizes for all mechanisms. Mainly to have DEBUG log fewer warnings.

auth: Use special AUTH_SUBSYS_DB/MECH parameters as auth_request_log*() subsystem. This avoids hardcoded strings all over the place and also allows assigning the correct passdb/userdb name for log messages generated by generic passdb/userdb code, which doesn't know exactly where it was called from.

auth: Removed unnecessary auth_request callback and context uses. --HG-- branch : HEAD

Removed MEMBER() macro. Require C99 style struct initializer. --HG-- branch : HEAD

Renamed headers to prevent collision if they were flattened on an install. --HG-- branch : HEAD

auth: Code cleanup for specifying what passdb features auth mechanisms need. --HG-- branch : HEAD

All password schemes can now be encoded with base64 or hex. The encoding is ".b64", ".base64" or ".hex" suffix in the scheme, eg. {plain.b64}. Password scheme verification function can now be set to NULL, in which case the verification is done by generating a new crypted password from given plaintext password and comparing it. --HG-- branch : HEAD

Removed enum passdb_credentials. Use scheme strings directly instead. This makes it possible to implement new mechanisms in plugins. --HG-- branch : HEAD

Reverted accidental commit. This code isn't ready yet. --HG-- branch : HEAD

Moved all storage destruction code to mail-storage.c and made destroy() optional. Removed set_callbacks(). Made autodetect() optional. --HG-- branch : HEAD

Added OTP and S/KEY authentication mechanisms. Patch by Andrey Panin. --HG-- branch : HEAD