Merge topic 'cmake-gui-incidental-errors'

d1792c48d5 cmake-gui: Suppress incidental error messages while choosing build tree
6f0ad398f1 cmake-gui: Clarify "Open Project" button implementation details

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Juan Ramos <cmake@jpr.mozmail.com>
Merge-request: !10448