doc update: add legal notes

from a long time ago:
http://lists.nongnu.org/archive/html/mingw-cross-env-list/2011-03/msg00107.html
package qtbase: disable mysql detection

fixes #325
mxe-activate: fix tools path and target list
Merge commit '9d64a57b431cd33a94ed0496ee9de6fc740eae79' into my

* commit '9d64a57b431cd33a94ed0496ee9de6fc740eae79':
  mxe-activate: fix tools path and target list
  package qtbase: disable mysql detection
  doc update: add legal notes