slow shutdown on uninstall

InnoDB implements various levels of "fast shutdown", from the slowest when all logs are applied to data, to the crash-like, which causes a full recovery run on the next start.

The default is 1, "fast". But this works best if the server of exactly the same version is used for the next start.

On upgrades the slow shutdown is the safest. Redo log format used to change between versions in the past and it has happened that after the upgrade the server was not able to start (or, worse, corrupted the data).

In fact, it's generally safer to use a slow shutdown when the server is uninstalled. RPM/DEB before-uninstall (preun, prerm) scriptlet should always use the slowest and safest shutdown method.

Implementation ideas:

• set global @@innodb_fast_shutdown=0
• SHUTDOWN SLOW
• SIGTERM for normal shutdown, SIGQUIT for slow (and SIGKILL for fast )