add comments to SourceOwner and JobOwner
add copyright notice to new source file
add examples showing `min list` and `max list`
catch more precise exception type in RecentFileSubmenu
Merge pull request #597 from NetLogo/recent-files-submenu

catch more precise exception type in RecentFileSubmenu
Allow variable watchers to remove themselves
document how `set breed` interacts with shapes
Merge commit '8ab633' into modelruns

Conflicts:
	headless/src/main/org/nlogo/agent/World.java
	src/main/org/nlogo/app/RecentFilesMenu.scala