[PATCH] fix segfault with DO and plperl/plperlu

If you do:

# DO $do$ 1; $do$ LANGUAGE plperlu;
# DO $do$ 1; $do$ LANGUAGE plperl;

You get a segfault as we try to SvREFCNT_dec(...); for the wrong
interpreter.  To fix push down the restore_context() so that we do the
above on the correct perl interpreter.
--
 *** a/src/pl/plperl/plperl.c
--- b/src/pl/plperl/plperl.c
***************
*** 1154,1170 **** plperl_inline_handler(PG_FUNCTION_ARGS)
  	PG_CATCH();
  	{
  		current_call_data = save_call_data;
- 		restore_context(oldcontext);
  		if (desc.reference)
  			SvREFCNT_dec(desc.reference);
  		PG_RE_THROW();
  	}
  	PG_END_TRY();

current_call_data = save_call_data;
- restore_context(oldcontext);
if (desc.reference)
SvREFCNT_dec(desc.reference);

error_context_stack = pl_error_context.previous;

--- 1154,1170 ----
  	PG_CATCH();
  	{
  		current_call_data = save_call_data;
  		if (desc.reference)
  			SvREFCNT_dec(desc.reference);
+ 		restore_context(oldcontext);
  		PG_RE_THROW();
  	}
  	PG_END_TRY();

current_call_data = save_call_data;
if (desc.reference)
SvREFCNT_dec(desc.reference);
+ restore_context(oldcontext);

error_context_stack = pl_error_context.previous;