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 remote-tracking branch 'origin/5.0.x' into headless

Conflicts:
	docs/dictionary.html
	src/main/agent/World.java
	src/main/org/nlogo/app/RecentFilesMenu.scala
	src/test/org/nlogo/headless/TestAgentVariableObservers.scala