Bug 677823 - Shift + mouse click to link all layers does not work

This got lost during layer group porting, reimplement it, but restrict
"all layers" to the clicked layer's branch in the tree.
(cherry picked from commit 67b5a509b6c830e59f0f9edaae78899afc0ec1c8)
Bug 677974 - GIMP suggests XCF as default export format

Only auto-add .xcf if it's a save (not an export) dialog, instead do
not auto-add anything and ask the user to enter an extension, that's
less mysterious than saving in the last-exported format which the user
maybe doesn't remember or want.
(cherry picked from commit 2f8d45611cb5f9bb90280c20f84f4a70ce7f4050)
app: get the help_id from the right action in gimp_editor_add_action_button()
(cherry picked from commit 4fbf01baefb346826b3895d47692519d24274248)
metadata: fix length passed to base64 decoder
(cherry picked from commit a4cd8637af7e29a3b78fda6034aa1889df050540)
Updated Spanish translation
Updated Slovenian translation
Updated 2 Greek translations
Bug 677375: tools do not strictly follow mouse...

pointer (missing motion events)

Disable calls gimp_help_set_help_data for shell->canavs
Updated Polish translation
Installer: allow override of system-wide configuration files with custom
versions during install
Installer: oops, remove duplicate function
Installer: fix permissions, add .gitignore
Installer: display a warning when color depth < 32BPP
Bug 677040: PDF export does not appear to handle font size...

...correctly unless image flattened

Font size was wrong unless in pixels and
gimp_drawable_type returns a GimpImageType
app: compress motion events up to the first release event

I'm not sure if it'd be better to compress only sequence
of contiguous motion events, thinking to the case of anticipating
a motion event before a modifier key press/release.
Updated italian translation.
Updated Finnish translation by Janne Peltonen.
Updated po-tips Finnish translation by Janne Peltonen.
Bug 679082: Crash after using Rotate tool
Updated Polish translation