app: re-enable and port the display shell mask rendering code

for the ported foreground select tool. Untested!
Merge branch 'master' of git://git.gnome.org/gimp
app: sense the input format in gimp:mask-components

because it can work on RGBA and R'G'B'A without conversions.
app: remove prepare() implementations from all layer mode operations

so the one in GimpOperationPointLayerMode is used which can switch
between RGBA and R'G'B'A.
app: some more precondition checks in gimpoverlaychild.c
app: accidentially removed a function's return type
app: add gimp_drawable_get_linear() which currently always returns FALSE

Add "linear" parameter to GimpApplicator. Pass the drawable's "linear"
to the applicator, and to all calls to gimp_gegl_mode_node_set_mode(),
instead of hardcoding FALSE everywhere.
app: fix various artifacts of the cancas' overlay children

gimp_overlay_child_size_allocate(): invalidate the old and new
position of the child, and simplify the code by calling our own
invalidate() function instead of duplicating its code.

gimp_overlay_child_expose(): process pending updates on the overlay
child's offscreen window before getting its pixmap.
app: remove the manual double buffering from the canvas

It is messing with overlay widgets. Is was effectively disabled since
cairo tool drawing was introduced, but not completely.
app: remove the image map tool overlay before hiding it again

Which means I have given up finding that last bug (for now).
Bug 699100 - Move tool: space-bar inhibits function of Move tool

Don't try to switch to the move tool if the move tool is already active.
Also never bail out early from gimp_display_shell_space_pressed() so we
don't end up in an inconsistent state.
plugin: Fix gih exporter to default first rank equal to number of cells
app: small optimization in gimp_operation_normal_mode_process()

Move some calculations out of the R,G,B loop, including a floating
point division, now there is only one division left per pixel.
app: GimpContainerEntry's text is red when not a valid item.

If the selected item in a GimpContainerEntry is invalid, or else when the entry
is being updated, the text shows in red.
Merge branch 'master' of git://git.gnome.org/gimp
add functionality phase 2.0