Misc changes

This is a similar pull request as https://github.com/divipp/lensref/pull/1 .  After these changes, the following warnings remain:

```
Building lgtk-0.9...
Preprocessing library lgtk-0.9...
[1 of 8] Compiling Data.LensRef.Default ( src/Data/LensRef/Default.hs, dist/build/Data/LensRef/Default.o )
[2 of 8] Compiling LGtk.Effects     ( src/LGtk/Effects.hs, dist/build/LGtk/Effects.o )
[3 of 8] Compiling LGtk.Key         ( src/LGtk/Key.hs, dist/build/LGtk/Key.o )
[4 of 8] Compiling LGtk.Widgets     ( src/LGtk/Widgets.hs, dist/build/LGtk/Widgets.o )
[5 of 8] Compiling LGtk.Render      ( src/LGtk/Render.hs, dist/build/LGtk/Render.o )

src/LGtk/Render.hs:73:5: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for ‘<>’: Patterns not matched: (X _) (X _)

src/LGtk/Render.hs:80:5: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for ‘flipp’: Patterns not matched: X _
[6 of 8] Compiling LGtk.Backend.Gtk ( src/LGtk/Backend/Gtk.hs, dist/build/LGtk/Backend/Gtk.o )
[7 of 8] Compiling LGtk.Backend.GLFW ( src/LGtk/Backend/GLFW.hs, dist/build/LGtk/Backend/GLFW.o )

src/LGtk/Backend/GLFW.hs:328:33: Warning:
    Pattern match(es) are non-exhaustive
    In a case alternative:
        Patterns not matched:
            Label _
            Button _ _ _ _
            Checkbox _
            Combobox _ _
            ...
[8 of 8] Compiling LGtk             ( src/LGtk.hs, dist/build/LGtk.o )
In-place registering lgtk-0.9...
Preprocessing executable 'lgtkdemo' for lgtk-0.9...
[ 1 of 11] Compiling LGtk.ADTEditor   ( lgtkdemo/LGtk/ADTEditor.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/ADTEditor.o )
[ 2 of 11] Compiling Data.Equivalence.Persistent ( lgtkdemo/Data/Equivalence/Persistent.hs, dist/build/lgtkdemo/lgtkdemo-tmp/Data/Equivalence/Persistent.o )

lgtkdemo/Data/Equivalence/Persistent.hs:108:19: Warning:
    Defined but not used: ‘rs’
[ 3 of 11] Compiling LGtk.Demos.Maze.Types ( lgtkdemo/LGtk/Demos/Maze/Types.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/Maze/Types.o )
[ 4 of 11] Compiling LGtk.Demos.MazeGen ( lgtkdemo/LGtk/Demos/MazeGen.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/MazeGen.o )
[ 5 of 11] Compiling LGtk.Demos.Maze.Maze ( lgtkdemo/LGtk/Demos/Maze/Maze.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/Maze/Maze.o )
[ 6 of 11] Compiling LGtk.Demos.Maze  ( lgtkdemo/LGtk/Demos/Maze.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/Maze.o )
*~

lgtkdemo/LGtk/Demos/Maze.hs:107:9: Warning:
*~
    Pattern match(es) are non-exhaustive
    In an equation for ‘genMaze’:
        Patterns not matched: (#x, _) with #x `notElem` [0#, 1#]
[ 7 of 11] Compiling LGtk.Demos.TEditor ( lgtkdemo/LGtk/Demos/TEditor.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/TEd*~
itor.o )

lgtkdemo/LGtk/Demos/TEditor.hs:30:9: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for ‘get’:
        Patterns not matched:
            (ghc-prim:GHC.Types.I# #x, _) with #x `notElem` [0#, 1#]
            (ghc-prim:GHC.Types.I# 1#, ElemsNil)
            (ghc-prim:GHC.Types.I# 1#, ElemsCons _ ElemsNil)
            (ghc-prim:GHC.Types.I# 1#,
             ElemsCons _ (ElemsCons _ (ElemsCons _ _)))
[ 8 of 11] Compiling LGtk.Demos.IntListEditor ( lgtkdemo/LGtk/Demos/IntListEditor.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/IntListEditor.o )

lgtkdemo/LGtk/Demos/IntListEditor.hs:90:1: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for ‘listEditor’: Patterns not matched: _ [] _
[ 9 of 11] Compiling LGtk.Demos.Tri   ( lgtkdemo/LGtk/Demos/Tri.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/Tri.o )
[10 of 11] Compiling LGtk.Demos.Main  ( lgtkdemo/LGtk/Demos/Main.hs, dist/build/lgtkdemo/lgtkdemo-tmp/LGtk/Demos/Main.o )

lgtkdemo/LGtk/Demos/Main.hs:170:36: Warning:
    Pattern match(es) are non-exhaustive
    In a case alternative:
        Patterns not matched:
            ghc-prim:GHC.Types.I# #x with #x `notElem` [0#, 1#, 2#, 3#, 4#]
[11 of 11] Compiling Main             ( lgtkdemo/Main.hs, dist/build/lgtkdemo/lgtkdemo-tmp/Main.o )
Linking dist/build/lgtkdemo/lgtkdemo ...
[hsenv]~/oss/divipp/lgtk$ cb
Building lgtk-0.9...
Preprocessing library lgtk-0.9...
In-place registering lgtk-0.9...
Preprocessing executable 'lgtkdemo' for lgtk-0.9...
```