Fixed some cases that didn't work with > 4G buffers.
Fixed compiler warnings


include/mysql_com.h:
  Avoid compiler warning with strncmp()
sql-common/client.c:
  Fixed long comment; Added ()
sql/filesort.cc:
  Fix code to get filesort to work with big buffers
sql/sys_vars.cc:
  Fixed some cache variables that could be set to higher value than the size_t
  Limit query cache to ULONG_MAX as the query cache buffer variables are ulong
storage/federatedx/ha_federatedx.cc:
  Remove not used variable
storage/maria/ha_maria.cc:
  Fix that bulk_insert() works with big buffers
storage/maria/ma_write.c:
  Fix that bulk_insert() works with big buffers
storage/myisam/ha_myisam.cc:
  Fix that bulk_insert() works with big buffers
storage/myisam/mi_write.c:
  Fix that bulk_insert() works with big buffers
storage/sphinx/snippets_udf.cc:
  Fixed compiler warnings