Implement the DO statement to support execution of PL code without having

 Implement the DO statement to support execution of PL code without having
 to create a function for it.
 
 Procedural languages now have an additional entry point, namely a function
 to execute an inline code block.  This seemed a better design than trying
 to hide the transient-ness of the code from the PL.  As of this patch, only
 plpgsql has an inline handler, but probably people will soon write handlers
 for the other standard PLs.
 
 In passing, remove the long-dead LANCOMPILER option of CREATE LANGUAGE.
 
 Petr Jelinek