Printing is only available in GTK versions >= 2.10. We can only embed
the page setup dialog on GTK >= 2.18, so on a GTK version less than
that, we must use a separate page setup dialog.

In GTK, printing is usually done one page at a time, so also modify
printing.c to allow printing of a single page at a time.

Create a separate drawing API for drawing to the screen and for
printing. Create a vtable for functions which need to be different
depending on whether they were called from the printing or drawing
API.

When a function is called from the printing API, it is passed a
separate instance of the frontend than if it were called from the
drawing API. In that instance of the frontend, an appropriate vtable
is available depending on whether it was called from the printing or
drawing API.

The low-level functions used for printing are enabled even if printing
is not enabled. This is in case we ever need to use them for something
other than printing with GTK. For example, using Cairo as a printing
backend when printing from the command line. Enabling the low-level
functions even when GTK printing is not available also allows them to
be compiled under as many build settings as possible, and thus lowers
the chance of undetected breakage.

Move the definition of ROOT2 from ps.c to puzzles.h so other files can
use it (gtk.c needs it for hatching).

Also add myself to the copyright list.

[Committer's note: by 'printing', this log message refers to the GTK
GUI printing system, which handles selecting a printer, printing to a
file, previewing and so on. The existing facility to generate
printable puzzles in Postscript form by running the GTK binaries in
command-line mode with the --print option is unaffected. -SGT]

This is the main bulk of this boolification work, but although it's
making the largest actual change, it should also be the least
disruptive to anyone interacting with this code base downstream of me,
because it doesn't modify any interface between modules: all the
inter-module APIs were updated one by one in the previous commits.
This just cleans up the code within each individual source file to use
bool in place of int where I think that makes things clearer.

This commit removes the old #defines of TRUE and FALSE from puzzles.h,
and does a mechanical search-and-replace throughout the code to
replace them with the C99 standard lowercase spellings.

Not many changes here: the 'dotted' flag passed to print_line_dotted
is bool, and so is the printing_in_colour flag passed to
print_get_colour. Also ps_init() takes a bool.

line_dotted is also a method in the drawing API structure, but it's
not actually filled in for any non-print-oriented implementation of
that API. So only front ends that do platform-specific _printing_
should need to make a corresponding change. In-tree, for example,
windows.c needed a fix because it prints via Windows GDI, but gtk.c
didn't have to do anything, because its CLI-based printing facility
just delegates to ps.c.

I've also added that warning option and -Werror to the build script,
so that I'll find out if I break this property in future.

I went through all the char * parameters and return values I could see
in puzzles.h by eye and spotted ones that surely ought to have been
const all along.

new function in the drawing API which permits the display of text
from outside basic ASCII. A fallback mechanism is provided so that
puzzles can give a list of strings they'd like to display in order
of preference and the system will return the best one it can manage;
puzzles are required to cope with ASCII-only front ends.

[originally from svn r8793]

draw dotted lines. No puzzle yet uses this, but one's about to.

[originally from svn r8453]

request either of hatching or halftoning, and also choose which to
supply as a fallback when printing in colour.

[originally from svn r7976]

midend_rewrite_statusbar() and check the result against the last
string returned. This is now done centrally in drawing.c, and the
front end status bar function need only do what it says on the tin.

While I'm modifying the prototype of drawing_init(), I've also
renamed it drawing_new() for the same reason as random_new() (it
_allocates_ a drawing object, rather than just initialising one
passed in).

[originally from svn r6420]