Debian package: Add XULRunner 20 compatibility
Debian package: consistently use "touch $@" for stamp files
Debian package: use dh_auto_{build,clean}
Debian package: Don't clean up stamp files manually

This is already done by dh_clean + debhelper compatibility level 7
Debian package: clean up rules file

Remove unnecessary comments and blank lines. Also add some blank lines
to gather related lines together in blocks.
Debian package: Use more debhelper magic

No more manual copying, symlinking or directory creating.
Debian package: Use sed inline edits in combination with dh_install
Debian package: Use variable for common path in debian/rules
Debian package: Bump debhelper compatibility to 9

Remove inclusion of buildflags.mk from debian/rules, no more needed.
Debian package: Switch to a dh style debian/rules
Debian package: clean up changelog entry
Makefile: Only set CFLAGS if not already set
Debian package: Mention changed CFLAGS handling in debian/changelog
Prevent our download manager from being overriden when Conkeror is run via firefox -app
cache: switch to an asynchronous interface for opening and clearing cache entries, as the synchronous interface supported by nsICacheSession doesn't seem to work
This fixes mime-type-override.
hints: ensure that dead DOM objects don't prevent us from leaving a hints interaction
content_handler_view_as_text: update to async cache interface
reinit: clear startup-cache before calling load_rc