Loads packages from pkg_resources entry points
Merge branch 'master' into 'pkg-as-setuptools-plugins'
Fills in _available_packages early
Merge branch 'master' into 'pkg-as-setuptools-plugins'
Fixes bug with nested packages
Don't check package structure for plugins
Removes unused MultiLineWidget, unused since 2009

Last usage removed by 63aa48e7.
Removes QTabBarDetachButton, unused since 2011

Last usage removed by 72884448.
Removes unused imports from common_widgets
Merge branch 'pkg-as-setuptools-plugins' into 'master'
Fixes TestImports#test_package()
Uses assertIn() in test
Adds -v command line flag for debugLevel
Adds __repr__() to module registry exceptions