Fix debugging on EDB with latest pldebugger

Thanks to recent changes I made to the pldebugger server-side functions,
the EDB-specific parts of pldebugger are now linked into the same
plugin_debugger.so library as the PL/pgSQL parts. It used to produce a
separate plugin_spl_debugger.so library, but that was inconvenient. For
example if you had a call stack that contained both PL/pgSQL and EDB-SPL
functions, you could not display both of them in the same debugger session.

That's now been changed in pldebugger, but now pgAdmin refuses to debug
SPL functions because it doesn't see plugin_spl_debugger.so in
shared_preload_libraries line. Here's a patch that teaches pgAdmin that
plugin_debugger.so now contains all that's needed or debugging SPL code.

I'm actually not sure it's a good idea to require
shared_preload_libraries to contain the library; much of the debugging
functionality is quite usable without that. If you load the library in a
single session, you can set local breakpoints and debug in that session,
for example. But this patch doesn't change that.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com