Rename mysql_connect() function to mysql_fdw_connect().

On MariaDB, mysql.h do have function named mysql_connect()
conflicting with our version.  So rename it.

Reported on GitHub through pull request #145 by
Glyn Astill (glynastill).  Another user, Михаил (mkgrgis),
also requested these changes.

Glyn Astill, revised by Jeevan Chalke.

connection.c

@@ -119,7 +119,7 @@ mysql_get_connection(ForeignServer *server, UserMapping *user, mysql_opt *opt)
 
 	if (entry->conn == NULL)
 	{
-		entry->conn = mysql_connect(opt);
+		entry->conn = mysql_fdw_connect(opt);
 		elog(DEBUG3, "new mysql_fdw connection %p for server \"%s\"",
 			 entry->conn, server->servername);
 
@@ -195,7 +195,7 @@ mysql_release_connection(MYSQL *conn)
 }
 
 MYSQL *
-mysql_connect(mysql_opt *opt)
+mysql_fdw_connect(mysql_opt *opt)
 {
 	MYSQL	   *conn;
 	char	   *svr_database = opt->svr_database;

mysql_fdw.h

@@ -345,7 +345,7 @@ extern void mysql_deparse_truncate_sql(StringInfo buf, Relation rel);
 /* connection.c headers */
 MYSQL *mysql_get_connection(ForeignServer *server, UserMapping *user,
 							mysql_opt *opt);
-MYSQL *mysql_connect(mysql_opt *opt);
+MYSQL *mysql_fdw_connect(mysql_opt *opt);
 void mysql_cleanup_connection(void);
 void mysql_release_connection(MYSQL *conn);