a few requests based on developing plpgsql_lint - maybe ToDo points

Hello

the basic issue is deployment of plpgsql plugins - they needs to
include "plpgsql.h", but this include file is not public. Next
significant issue is impossibility to serialize plpgsql plugins. Only
one should be supported. A limit is a access to persistent data via
estate->plugin_info. Others issues are not too significant - but can
to simplify a plugin development

1. move plpgsql.h to shared "include" directory
2. allow more active plpgsql plugins in one time
3. allow access to function's result or statement's result - minimum
is access to rc
4. allow to create a temporary copy of plpgsql's statements and
execute this copy - not original
5. a hooks for execution handler's calls - is not possible to handle a
situation, when function ends with exception
6. a hook for validation
7. publish exec_prepare_plan with possibility to add hook to this function

Regards

Pavel Stehule