Close #7108

Close #6466

Close #6209

This should fix LP#947156.

This mostly reverts commit 7240444d.
This broke threading rules for Qt4 GUI.

Conflicts:
	modules/gui/qt4/dialogs/external.cpp

This eases matching of unknown keys.

Also do not save garbage, especially pointers, in the plugin cache.

This hinders the following commits. This was only used in a single
plugin on a single platform, and was poorly designed.

Until config_GetPszChoices() learns to load modules when needed, any
module with a list callback must be loaded at all times.

The code previously assumed that plugins with list callbacks also had
action callbacks. This is not true.

macosx: dynamically create context and main sub menu for playlist table header selection, Simplifications in existing code

Regression from d70cda88.

The layout of struct addrinfo is variable (notably because of RFC5014),
so copying hints is brittle.