backport of #720 to describe context in exception views

Conflicts:
	CONTRIBUTORS.txt
add removal of ``pyramid.debug_templates`` to "What's New"
Merge pull request #723 from ericrasmussen/1.3-branch

add removal of ``pyramid.debug_templates`` to "What's New"
remove duplicate reference to ``Configurator.scan`` method
Merge pull request #724 from ericrasmussen/1.3-branch

remove duplicate reference to ``Configurator.scan`` method