Also search for mariadb_config on compile

libmariadb-client-lgpl-dev in newly released Debian stable (jessie)
ships `/usr/bin/mariadb_config`.

Author: ctrochalakis

ext/mysql2/extconf.rb

@@ -36,7 +36,7 @@ def asplode lib
   /usr/local/lib/mysql5*
 ].map{|dir| "#{dir}/bin" }
 
-GLOB = "{#{dirs.join(',')}}/{mysql_config,mysql_config5}"
+GLOB = "{#{dirs.join(',')}}/{mysql_config,mysql_config5,mariadb_config}"
 
 # If the user has provided a --with-mysql-dir argument, we must respect it or fail.
 inc, lib = dir_config('mysql')