currently plugin names should be globally unique in the server.
In fact, they only need to be unique within a plugin type. There is no reason
why there can not be a fulltext parser plugin "csv" and storage engine plugin "csv".
This task allows plugins with the same name to be installed as long as they are
of different plugin type. It also adds
INSTALL plugin_type PLUGIN name SONAME "path";
command (e.g. INSTALL FTPARSER PLUGIN csv SONAME "csv.so"), to resolve the case
when one .so has two plugins with the same name.