move wayward functions to appropriate files and/or classes

Identify and rehome functions that currently live in counterintuitive locations. Examples include session, thread, table and cache management functions living in drizzled/sql_base. This helps to consolidate core classes like Session and Table. The scope of this blueprint is drizzled/sql_xxxx files such as sql_base and sql_parse and the various destination files such as drizzled/session.* and table.*.