BUG: Fix logic checking for readonly folder in writeToMRB method

Following r22395 "qSlicerSceneWriter::writeToMRB" has been updated to
check is the MRB file to be written was writable or not, the test was
always failing since the file itself wasn't existing.

This commit implement the appropriate logic by checking if the destination
folder where the MRB should be saved is writable.

This commit also fix the test "test_slicer_util_save.test_saveSceneAsMRB"

See #3242

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22401 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Fix unused variable warnings

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22402 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix loading of ".mgh.gz" file in py_nomainwindow_test_slicer_mgh

Method "IsCompressedFilename" has been copied from the improved fork
of MGHImageIO maintained by ITK folks (Hans).
See https://github.com/Slicer/itkMGHImageIO

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22403 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix "py_nomainwindow_test_slicer_mgh" allowing "mgh" to be saved

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22404 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Add ".mgh.gz" to the list of FreeSurferModelOverlay read file types.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22405 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Exclude html extension from git hook line lengths check

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22406 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Update Documentation to 4.3

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22407 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Slicer 4.3.0

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22408 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Begin post-4.3.0 development

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22409 3bd1e089-480b-0410-8dfb-8563597acbee