MDEV-9278 - Debian: the Lintian complains about "shlib-calls-exit" in ha_spider.so
Handlersocket handles errors in a way that it aborts program execution. In most
cases it is done via abort(). One exception was host/service resolution failure,
which was aborted with exit().
As a workaround replaced this exit() with abort() for symmetry with other error
handling.
- Fixed compiler errors
- Modified Makefiles to be part of plugin directory
- Some minor changes in database.cpp to use the new MariaDB handler interface
