Merges the latest Shotwell master into the faces branch and concludes Valentín Barros Puertas's Google Summer of Code work for the summers of 2011 and 2012. Valentín is responsible for the entire Faces tool user experience, data model, and the automated face detection feature. The features in the faces branch that are not present in Shotwell master are almost entirely the result of Valentín's work. This work was conducted under the mentorship of Adam Dingle and Lucas Beeler in 2011 and Lucas Beeler in 2012. Both Lucas and Adam are members of the GNOME Foundation, which generously sponsored Valentín's work.

Makes the 'extended information' window display the path to the master file, rather than the currently-displayed one; closes #4137 .

Causes a null string set to be considered equal to an empty one, since it follows that they both have 0 elements. Closes #4297.

Prevents the application from inappropriately renaming 'sister' JPEG files -and- forces the application to always prefer the camera development over the embedded one if it's available; closes #4149.

This is technically not required for building Shotwell, but we
want to move automated packaging builds now and in the future
to newer versions.

Corrects a problem in which pushing the left arrow key mapped to a rightward transition to the previous photo in the slideshow view. Closes #6258.

Displays a more user-friendly error message when the Vala compiler is not present or is the wrong version. Closes #1856.

Conflicts:
	Makefile
	src/folders/Page.vala
	src/library/LibraryWindow.vala
	src/library/mk/library.mk
	src/util/ui.vala

Fixes a build system issue in which the GSchema XML files would not be properly recompiled. Closes #6178.

Copies the Tumblr publishing service icon to the appropriate system resource directory when "make install" is invoked. Closes #6242.

*...if and only if the 'stale' image is not a user-supplied/camera-created one (to wit, the JPEG file of a RAW+JPEG pair).

Prevents the library directory itself from getting deleted as we walk up the parent tree; closes #6241.

Also moves some code around so regeneration for both stills and videos happens in the same spot, improving code navigability.

Increases MIN_VALAC_VERSION to the earliest version of valac that ships with vapi files for GStreamer 1.0.

Prevents file discovery and metadata writing from starting before ALL initialization, including tag list population, is completed.

Fixes #5992.

Modifies RAW photo development logic to properly copy original photo metadata into generated developments. Closes #4372.