Separates per backend type from per backend database initialization
and startup. Also supports per type / per backend shutdown.
New frontend startup/shutdown routines are also provided:
slap_init() slap_startup() slap_shutdown() slap_destroy()
New frontend->backend startup/shutdown is managed by:
backend_init() backend_startup() backend_shutdown backend_destroy
backend_init() now calls bi_init() to initial all function pointers
for the backend (excepting bi_init() which is now the only hardcoded
entry point). New entry points are detailed in slap.h struct
backend_info. backend_info is a per database type structure.
Besides the new startup/shutdown entry points, the new interface
also supports per backend type configuration options. One could have:
backend bdb2 (new Berkeley DB 2 backend)
bdb2_home /directory
database bdb2
...
*** This code is fairly experimental ***
*** Much cleanup and testing is still needed ***
see slap.h for details on struct backend_db and backend_info.
