first add newly loaded plugin to the list then invoke _PG_init

[mickiewicz]

Hi All,
I'm working on C plugin for Postgres (ver. 10). One of the thing which I 
need is to automatically add some SQL functions from the plugin during 
its initialization ( inside _PG_init method ). It means that during 
loading libmyplugin.so _PG_init calls SPI_execute( "CREATE FUNCTION 
fun() RETURNING void()  AS '$libdir/libmyplugin.so', 'fun' LANGUAGE C" 
), what leads to recursive call of _PG_init. It seems that the problem 
is with adding a plugin to the list after the execution of _PG_init, not 
before: 
https://github.com/postgres/postgres/blob/2c0cefcd18161549e9e8b103f46c0f65fca84d99/src/backend/utils/fmgr/dfmgr.c#L287 
. What do You think about changing this and add a newly loaded plugin to 
the list and then execute its _PG_init ? This change will help to keep 
consistency between plugin expectation about database structure (about 
tables, functions, etc.) without delivery additional SQL scripts - 
plugin itself will be able to prepare all the required things.

Best Regards,
Marcin