New puzzle! Or rather, new-ish, because this one has been lying around

in the 'unfinished' directory for a while, and has now been finished
up thanks to James Harvey putting in some effort and galvanising me to
put in the rest. This is 'Pearl', an implementation of Nikoli's 'Masyu'.

The code in Loopy that generates a random loop along grid edges to use
as the puzzle solution has been abstracted out into loopgen.[ch] so
that Pearl can use it for its puzzle solutions too. I've also
introduced a new utility module called 'tdq' (for 'to-do queue').

[originally from svn r9379]

pearl.R

@@ -0,0 +1,23 @@
+# -*- makefile -*-
+
+PEARL_EXTRA    = dsf tree234 grid penrose loopgen tdq
+
+pearl          : [X] GTK COMMON pearl PEARL_EXTRA pearl-icon|no-icon
+pearl          : [G] WINDOWS COMMON pearl PEARL_EXTRA pearl.res?
+
+pearlbench     : [U] pearl[STANDALONE_SOLVER] PEARL_EXTRA STANDALONE m.lib
+pearlbench     : [C] pearl[STANDALONE_SOLVER] PEARL_EXTRA STANDALONE
+
+ALL += pearl[COMBINED] PEARL_EXTRA
+
+!begin gtk
+GAMES += pearl
+!end
+
+!begin >list.c
+    A(pearl) \
+!end
+
+!begin >wingames.lst
+pearl.exe:Pearl
+!end