Fix the "readonly" option of IMPORT FOREIGN TABLE

When set to "false", it would still create read-only foreign tables.

This closes #330 reported by Jacob Roberts.

CHANGELOG

@@ -24,6 +24,9 @@ Version 2.2.0
     Since PostgreSQL's "numeric" does not know infinity, map these values
     to NaN in this case.  For "real" and "double precision" we can use the
     normal infinity values.
+  - The "readonly" option of IMPORT FOREIGN SCHEMA didn't work properly:
+    When set to "false", it would still create read-only foreign tables.
+    Reported by Jacob Roberts.
 
 Version 2.1.0, released 2018-10-01
   Enhancements:

oracle_fdw.c

@@ -2251,13 +2251,13 @@ oracleImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 		else if (strcmp(def->defname, "readonly") == 0)
 		{
 			char *s = ((Value *) (def->arg))->val.str;
-			if (pg_strcasecmp(s, "on") != 0
-					|| pg_strcasecmp(s, "yes") != 0
-					|| pg_strcasecmp(s, "true") != 0)
+			if (pg_strcasecmp(s, "on") == 0
+					|| pg_strcasecmp(s, "yes") == 0
+					|| pg_strcasecmp(s, "true") == 0)
 				readonly = true;
-			else if (pg_strcasecmp(s, "off") != 0
-					|| pg_strcasecmp(s, "no") != 0
-					|| pg_strcasecmp(s, "false") != 0)
+			else if (pg_strcasecmp(s, "off") == 0
+					|| pg_strcasecmp(s, "no") == 0
+					|| pg_strcasecmp(s, "false") == 0)
 				readonly = false;
 			else
 				ereport(ERROR,