fix build with MariaDB 10.2 headers

From: brianmario#1014

Author: AlexeyDemidov

ext/mysql2/client.c

@@ -54,7 +54,9 @@ static VALUE rb_hash_dup(VALUE other) {
  * variable to use, but MYSQL_SERVER_VERSION gives the correct numbers when
  * linking against the server itself
  */
-#ifdef LIBMYSQL_VERSION
+#if defined(MARIADB_CLIENT_VERSION_STR)
+  #define MYSQL_LINK_VERSION MARIADB_CLIENT_VERSION_STR
+#elif defined(LIBMYSQL_VERSION)
   #define MYSQL_LINK_VERSION LIBMYSQL_VERSION
 #else
   #define MYSQL_LINK_VERSION MYSQL_SERVER_VERSION
@@ -1297,6 +1299,10 @@ void init_mysql2_client() {
 #ifdef CLIENT_LONG_PASSWORD
   rb_const_set(cMysql2Client, rb_intern("LONG_PASSWORD"),
       LONG2NUM(CLIENT_LONG_PASSWORD));
+#else
+  /* HACK because MariaDB 10.2 no longer defines this constant,
+   * but we're using it in our default connection flags. */
+  rb_const_set(cMysql2Client, rb_intern("LONG_PASSWORD"), INT2NUM(0));
 #endif
 
 #ifdef CLIENT_FOUND_ROWS

ext/mysql2/mysql2_ext.h

@@ -15,12 +15,10 @@ typedef unsigned int    uint;
 
 #ifdef HAVE_MYSQL_H
 #include <mysql.h>
-#include <mysql_com.h>
 #include <errmsg.h>
 #include <mysqld_error.h>
 #else
 #include <mysql/mysql.h>
-#include <mysql/mysql_com.h>
 #include <mysql/errmsg.h>
 #include <mysql/mysqld_error.h>
 #endif