both a non-threaded libmysqlclient and a threaded libmysqlclient_r.


Makefile.am:
  - build libmysqlclient_r in a separate directory
include/global.h:
  - build libmysqlclient_r in a separate directory
libmysql/Makefile.am:
  - build libmysqlclient_r in a separate directory