Bug 715018 - Developer documentation on VBRs incorrect

Fix the order of fields, and improve some other parts.
Bug 701168 - Select | Shrink: A better label for "Shrink from image border"

Change the weird button labels in the shrink and border dialogs to
"Selected areas continue outside the image" and add tooltips.
Updated German translation
Updated italian translation
Bug 525705 - skip thumbnailing entirely on files with insufficient...

...read permissions

Apply modified patch from Sven Neumann which implements just that.
build/win: Upgrade libpng to 1.6.7
libgimpbase: add gimp_output_stream_[v]printf()

Temporary, to be removed when we depend on glib 2.40, which will
clearly be before gimp 2.10
initialize length to appease cppcheck

The code was technically correct previously: It wrote the uninitialized
length only as a placeholder to overwrite it later on. Yet it's better
to not confuse tools (or people) analysing the code. Besides that having
0 for the length in the file while the payload is being written may aid
debugging e.g. crashes in that code later on.
app: fix two typos
devel-docs: clarify where to announce a release in release-howto.txt
plug-ins: port file-csource to GIO
app: add G_GNUC_PRINTF() to places where the args are a va_list

The trick is to use G_GNUC_PRINTF (n, 0).
Bug 719560 - Build failure with freetype 2.5.1

Apply patch from su-v that fixes the freetype include to
the madness devised and recommended by freetype.
Bug 719593 - On clang, brush outline is not displayed

Don't access path_data->len after path_data has been freed.
app: add gegl:wind to Filters -> Distorts
build/win: Upgrade poppler to 0.24.4
Bug 719634 - Palette editor not working for New Palettes (cannot drop colors)

Allow to drop colors also on the palette view's parent viewport, so
colors can be dropped everywhere inside the scrolled window, also when
the palette view is invisible because it has zero colors. Also allow
dropping of palettes on the viewport to change the editor's active
palette.
Bug 719662 - plug-in-borderaverage returns a garbage alpha value

Return a fully opaque color instead of a random-memory alpha value.
app: a bunch of actions which should be inactive when there is no image
Fixed an error in the close-port function. Closes bug #719396.