Fixes the code style and improves the PHPDoc

The coding standard that best matches the used one is PSR2.
Nevertheless as the source code was originally written in PHP4 there
are still two types of warning messages that cannot be solved for now:

  * Method name is not in camel caps format.
  * Each class must be in a namespace of at least one level.
Code inspection: unused local variable
Code inspection: undefined variable
Code inspection: undefined method
Wrong method call

PGQInteractiveConsumer::finish_batch() calls PGQ::next_batch() instead
of PGQ::finish_batch()
Code inspection: unreachable statement
Code inspection: missing return statement
Declaring process_event() as an abstract method

It seems like method was not declared whereas class implementation
expects method to be overriden in child classes. Sounds like an
abstract method ;)
Code inspection: undefined field
Using relative paths in require_once directives

For a use without the PHP include_path, e.g. with an autoloader,
"require" directives must be declared with relative paths.
Adding missing method visibility