Portability fixes


mysql-test/r/func_str.result:
  Added test for ltrim and rtrim with NULL
mysql-test/t/func_str.test:
  Added test for ltrim and rtrim with NULL
sql/item_strfunc.cc:
  Streamlined code for trim, ltrim and rtrim
tests/client_test.c:
  Fixed wrong usage of %lld (not portable)