INSTALL PLUGIN *

InnoDB, XtraDB, PBXT (at least) come with a storage engine plugin and many
information_schema plugins in one .so file.

Currently one needs to install them all one by one.

INSTALL SONAME xxx

would be a more convenient way to install everything at once.

Additionally we introduce

UNINSTALL SONAME xxx

to be able to uninstall all these plugins with one statement.

As another bit of user-friendliness we'll allow one to specify .so/.dll names
without an extension. Simply "ha_example" instead of "ha_example.so" or
"ha_example.dll". This will allow users to write portable sql scripts and config
files, that work on Linux, Windows, Mac OS X, etc.