pgAdmin III: the debugger does not pre-populate default values for arguments

Hi,

The debugger, when it is invoked on a function or a procedure, provides a
dialogue box to fill up values for the arguments. In case the user has
created them with some default values assigned to some of the parameters,
then they would expect that the debugger pre-populates them with those
default values. This is not happening currently.

The attached patch provides this functionality.

We check if the "argdefvals" column exists in the output for the func/proc.
If it does, it gets tokenized and added to the corresponding wsArgInfo
object. These values then get displayed appropriately.

One side-effect of this feature is that earlier where non-default variables
appeared as empty, they will now appear with values "". This will happen
only if some arguments have defvals and some don't. We could have added code
to do away with "" entries, but then I thought it is possible for people to
provide "" as default values too. So we can live with this I think..

Regards,
Nikhils