Add support for the location change state machine and related
* src/ntl-types.h, src/ntl-uri-map.[ch], src/ntl-window-msgs.c, src/ntl-window.[ch]: Add support for the location change state machine and related notifications, to allow much better error handling. * src/ntl-view.[ch]: Catch client failures, also allow for active sensing of client death. * src/file-manager/fm-directory-view.c: Send progress notifications. * components/html/ntl-web-browser.c: Send progress notifications. Try to fix crashes caused by ending an error stream twice.