client/Makefile.am:
  Link mysqltest with mysys library
client/mysqltest.c:
  Add new commands to mysqltest:
   - remove_file
   - copy_file
   - file_exists
   - write_file
   - perl
mysql-test/r/mysqltest.result:
  Update result file
mysql-test/t/mysqltest.test:
  Add tests for new commands