Merge branch 'maint-2.4.2' of github.com:agda/agda into maint-2.4.2
[ fix ] Replaced BadConstructor by __IMPOSSIBLE__.
Merge branch 'maint-2.4.2'
[ new ] Interactive tactic development.
  Unsolved metas are now allowed inside an `unquote ...'.
[ fix ] Fixed annoying yellow on incomplete tactics.
[ hTags ] Add option to extend include path

And update Makefile accordingly.
Merge branch 'maint-2.4.2'
Merge remote-tracking branch 'origin/maint-2.4.2'

Conflicts:
	src/full/Makefile
	src/hTags/Main.hs