fixed ls_alias for OpenBSD as it lacks the -G switch
fix ls_alias for NetBSD as well
pin requests to 2.4.1 on travis

bug in requests 2.4.2 doesn't allow unicode URLs on Python 2
added comment on reason for seperate ls_alias for OpenBSD/NetBSD
forbid known-bad requests-2.4.2
Merge pull request #6625 from bsvh/master

Fix ls_alias for certain BSDs
Merge pull request #6630 from minrk/travis-requests-2.4.1

forbid broken requests-2.4.2 on travis
Clean up session class
Fix reference to session in notebook.js
Fix bugs introduced into session.js
Clean up kernel.js
Fix messages received by notification area
User correct check for whether kernel is running in tests
Fix session references in toolbar and menubar
Fix bugs in kernel.js
Fix shutdown test
Better respect for abstraction barriers
Move channels into their own object
Only set channels to null when they are fully closed
Fix kernel and session tests