patch 8.0.1516: errors for job options are not very specific

Problem:    Errors for job options are not very specific.
Solution:   Add more specific error messages.
diff --git a/src/globals.h b/src/globals.h
index 2504d2e..225e78a 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1437,6 +1437,8 @@
 EXTERN char_u e_invaddr[]	INIT(= N_("E14: Invalid address"));
 EXTERN char_u e_invarg[]	INIT(= N_("E474: Invalid argument"));
 EXTERN char_u e_invarg2[]	INIT(= N_("E475: Invalid argument: %s"));
+EXTERN char_u e_invargval[]	INIT(= N_("E475: Invalid value for argument %s"));
+EXTERN char_u e_invargNval[]	INIT(= N_("E475: Invalid value for argument %s: %s"));
 #ifdef FEAT_EVAL
 EXTERN char_u e_invexpr2[]	INIT(= N_("E15: Invalid expression: %s"));
 #endif