Improve OS X help: split back up into multiple files (thanks to
Halibut's new \cfg{html-local-head} directive), and add some CSS to
mimic the font choices of system help files.

[originally from svn r5194]
Help should have the shortcut Command-?.

[originally from svn r5195]
`make release' target, which builds a .dmg disk image in what
appears to be the approved Apple fashion.

[originally from svn r5197]
Ahem. Rogue copy and paste was causing preset menu items to go into
the Help menu rather than the Type menu. Fixed.

[originally from svn r5199]
Updates for OS X port (including updating copyright statements).

[originally from svn r5201]
Ahem. Lots of stuff, including the new OS X sources, was being left
out of the tarball by makedist.sh, causing the downloaded source
tree to fail mkfiles.pl. Worse still, the GTK Makefile wasn't
included, so people _needed_ to run mkfiles.pl! Both now fixed, I
think.

[originally from svn r5205]
Include code in midend.c to sanitise streams of mouse events so that
back ends can be assured of always receiving them in a sensible
sequence (button-down, followed by zero or more drags, followed by
button-up, and never changing button in the middle of such a
sequence). I have a suspicion this issue was the cause of the
mysterious Pattern grid updates seen by Dan during testing last
night.

[originally from svn r5208]
Sanitising the mouse input data was a good idea, but my
implementation sucked. Revise it completely.

[originally from svn r5209]
Need to impose a _maximum_ width on edit boxes, as well as a minimum
width; if allowed to resize to the text within them, they look
terribly silly when containing an entire Rectangles or Pattern game
ID.

[originally from svn r5210]
I've found NSView's setNeedsDisplayInRect: method, which is
obviously better than just calling setNeedsDisplay on the whole
thing...

[originally from svn r5258]
Fixes in grid generation for pedantic special cases when one or both
grid dimensions are very small.

[originally from svn r5390]
Stop the Pattern grid generation from generating an entire row or
column of the same colour (at least when the dimensions are big
enough to make this feasible). It's a little bit too easy otherwise!

[originally from svn r5391]
Oops. Just noticed that the Windows front end completely ignores the
`colour' parameter in draw_text().

[originally from svn r5507]
Initial checkin of `Solo', the number-placing puzzle popularised by
the Times under the name `Sudoku'.

[originally from svn r5660]
Visual C points out a couple of typos.

[originally from svn r5661]
Simplify clip region handling under Windows, which also makes Solo's
clipping policy work properly. I haven't proved why it didn't work
the previous way, but I have a good guess: I think that clip regions
are handled by reference. So I saved the old clip region out of the
DC, then did an IntersectClipRect, and then selected the old clip
region back in again - but the old clip region had never been
_de_-selected, because IntersectClipRect didn't change which object
was selected but rather it modified-in-place the one that already
was selected. So my attempt to restore the old clip region did
nothing whatsoever, and thus clipping to two different rectangles
during the same draw sequence failed. Now I'm completely destroying
the clip region during unclip(), which seems to work better.

[originally from svn r5662]
Doc tweaks for Solo.

[originally from svn r5665]
Introduce configurable symmetry type in generated puzzles, and drop
the default symmetry from order-4 down to order-2, which seems to
mitigate the excessively-full-grid problem by permitting more
freedom to remove stuff.

[originally from svn r5666]
Outstandingly cute mathematical transformation which allows me to
lose a lot of code duplication in nsolve while preserving efficiency.

[originally from svn r5667]
Various changes prompted by my boss taking an interest:
 - added a compilation option -DSTANDALONE_SOLVER which makes both
   of Solo's internal solvers accessible from the command line.
 - fix a bug in nsolve turned up by testing in this mode: it failed
   to iterate at all! Oddly, this massive improvement to the
   effectiveness of nsolve hasn't emptied the generated grids by
   very much.
 - add an extra mode of reasoning to my to-do list (which is the
   dual of one already there, so I'm kicking myself).

[originally from svn r5670]