Explicitly say that the mesh will be incorrect if the swapping failed

Fixed one more bug for degenerate, non-recombined extrusions, that could
lead to duplicate elements.

Fix seg fault in Read_SMS

New option pane ("Helpers") with text editor and web brower commands.

Fixed degenrate tets generation (oops!)

#ifdef some platform-specific stuff

Fix unsigned int warning

Better web browser command for Unix + generalized call (permit
multiple '%s').

typo

- Split File->Open into File->Open and File->New (i.e., the file
  chooser now only accepts existing files for File->Open)

- Added "Online documentation" help menu

Fine-tune system menu bar

better name for MacOS system menu bar option

Set max quality

some more mpeg encoders + params for higher quality

Better doc for Show/Hide

-histogram was broken in batch mode

Don't output STATUSxN messages in batch mode

"Curve" -> "Line"

Set vis_input::value() to "*" be default

couple of bugs from he mailing list

- Slightly reorganized the visibility browser window (the "toggle"
  behaviour in the input field was confusing)

- added Show and Hide commands in the parser to enable scripting of
  the visibility stuff

- Moved Visibility.{cpp,h} into Common/ to avoid dependencies with the
  Graphics library in the parser

Fix rare crash due to Fl_Widget::tooltip() not actually copying the
string.

Fixed bug in DecomposeInSimplex (need to set deleted non-simplex lists
to NULL)

Fixed missing exception handling for PluginManager::action() (this led to
a crash when General.DefaultPlugins==0).