Make DB use UTF-8 as default charset in unit tests.
SQL: drop host/service group memberships on instance start/stop.

This fixes #5507.
SQL: set empty string fields as NULL in the logs table.

This fixes #5613.
storage: handle infinity in metrics. This fixes #5648.
correlation: use a proper start time for issues created at startup.

This fixes #5471.
core: handle configuration reload failure. This fixes #5522.
core: shared_ptr now handles implicit pointer conversion. This
reduces code complexity (not that much).
doc: update.
core: added shared_ptr non-template default copy constructor and shared_ptr assignment operator.
core: simplification on misc::shared_ptr.
storage: handle infinity values in the rebuilder thread.

This refs #5648.
  dev: add the instances.outdated, services.real_last_hard_state and hosts.real_last_hard_state fields to the mysql database.
  dev: add a mecanism to update the instances, services and hosts fields when an instance didn't answer for a certain timeout time.
  dev: add the unitary test to test this mecanism.
  dev: Added sql CMakeList (forgotten from last commit).
  dev: Added doxygen for class stored_timestamp
  dev: Updating header guards.
SQL: minor style fixes.
Merge branch 'master' of http://git.centreon.com/centreon-broker
SQL: use a map for the outdated mecanism.
BBDO: add benchmark program against NDO.
NDO: propagate data commit when requested.
storage: graph infinity values are +/-INFINITY, not DBL_MIN/DBL_MAX.

This fixes #5648.