Update to experimental r13565

Minor pass of header cleanup

Code cleanup.

Super duper mega (fun!) commit: replaced encoding=utf-8 with fileencoding=utf-8 in all 1074 Vim modelines. The reason for this is that (a) setting the encoding isn't nice, and (b) Vim 7.3 (with modeline enabled) disallows it and pops up an error whenever you open any file with it ("invalid modeline"). Also corrected five deviant modestrings: * src/ui/widget/dock.cpp and src/ui/widget/dock.h: missing colon at the end * src/ui/dialog/tile.cpp: removed gratuitous second colon at the end * src/helper/units-test.h: removed gratuitous space before a colon * share/extensions/export_gimp_palette.py: missing textwidth=99 That's my geekiest commit yet.

Fundamentally reworked version of the 3D box tool (among many other things, this fixes bugs #168900 and #168868). See mailing list for details. Sorry for this single large commit but it was unfeasible to keep the history.

Rewrite of z-order code for 3D boxes, first stage (hopefully this is finally the right approach)

(Un-)Snapping of VPs by Shift-dragging; this makes it possible to separate perspectives and thus create new ones interactively

Move 3D axis manipulation functions to separate file