Add versort test based on manual page
Move modes/normal:start_dir_size_calc() to fileops

It's not related to normal mode and shouldn't be there.

Also add some comments, updated names and style a bit.
Move fileops:calc_dirsize() below its last use
Extract fileops:calculate_size()

Initiates background calculation of directory sizes.

Reduces code duplication.
Add ga and gA keys to visual mode

Thanks to geo909.
Taught ga/gA commands to handle selection

Thanks to geo909.
Move fileops:set_dir_size() below its last use
Merge branch 'enhance-ga-gA'

Added ga and gA keys to visual mode.

Taught ga/gA commands to handle selection.

Thanks to geo909.
Fix navigation to filtered-out files

E.g. from menus.  Cursor wasn't moved to the file.
Do not remember one more statusbar message
Merge branch 'fix-navigation-to-filtered-out-file'

Fix navigation to filtered-out files (e.g. from menus).  Cursor wasn't
moved to the file.

Also removed one more useless message from history of status bar
messages.