Implement Loadable Storage Engines
Storage Engines may be loaded by the the user (with appropiate privilege checks) with the following commands: INSTALL PLUGIN <name> SONAME "filename" (note, these are the commands introduced by the plugin framework, no new syntax was created for this worklog) As part of the work, the CSV and Example storage engines were altered to be plugable as per the MySQL plugin framework abi. The code now relies on the plugin framework to enumate builtin and loaded storage engines. Currently, unloading storage engines at run time is not advised.
Made use of the existing plugin framework. Simply used handlerton as storage engine specific plugin info. As part of the work, enum db_type was deprecated with preference to the handlerton The plugin framework was extended to permit built-in plugins and for the storage engine to use the plugin framework to enumerate all handlertons.