[ SEMANAGE 3 ] Common database code

[Ivan Gyurdiev <ivg2@xxxxxxxxxxx>]

This patch merges the handling of the default database with transaction 
management (enter_ro/exit_ro/exit_rw), and cache management, and puts 
that in common (polymorphed) code - database.c. It changes relay 
functions and internal invocation to use this code. In order to do that, 
the cache() function was exposed in the database interface, and now it 
must be called before other functionality dealing with records is used 
(called internally, of course).

Also, cleans up includes for relay functions (and removes unnecessary 
and obsolete defines of database backend - those relays should be 
backend independent).

Benefits:
- transaction enter/exit code is now shared for all databases, and can 
be easily changed
- this also removes duplicate code, and makes the per-backend database 
code simpler
- no need to write things like get_rtable/flush/drop_cache in the 
default database, which make no sense
- Note that the per-backend dbase functions are now reentrant-safe, 
which means that I can layer one on top of another if I want to
- this still doesn't let me call other database functions from an 
iterate() handler, but I think it might get us closer to this goal.

Attachment: libsemanage.dbase_common.diff.bz2
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