New info Hvy-Plastic

Island size is randomly chosen from the interval [1..2*is+1], with
expected value is.  Use two dice to roll the size instead of one.
This makes extreme sizes much less likely.
(cherry picked from commit 29d2f5ccfe)

info/Hvy-Plastic.t

@@ -0,0 +1,53 @@
+.TH Concept "Hvy-Plastic"
+.NA Hvy-Plastic "Special rules for Hvy Plastic 3"
+.LV Basic
+.s1
+Ship types are customized.  Better check show for the details.
+.s1
+Dreadnoughts are more heavily armored.  Frigates are more fragile.
+.s1
+Land unit types are heavily customized.  Better check show for the
+details.  Non-mechanized units are slower and more vulnerable,
+artillery firing ranges differ, few units are light (but troop
+transports and landing ships can carry non-light units).
+.s1
+Planes are tweaked somewhat.  show is your friend.
+.s1
+Heavy bombers can drop seamines.  Anti-sub planes can't.
+.s1
+Nukes are on sale, but nuclear plants are not.  Did I mention the show
+command?
+.s1
+Infrastructure is disabled.
+.s1
+Fortresses cost maintenance, like capitals.
+.s1
+Your refineries make less petrol from each barrel of oil than usual.
+.s1
+Natural resources gold, oil and uran deplete much slower than usual.
+A 100% gold resource contains 2500d, a 100% oil resource contains
+2500o, and a 100% uranium resource contains 500u.  Fully depleting a
+sector will take you several updates, and a small fraction of the
+resource contents will be lost.
+.s1
+Gold in mountains does not deplete at all.
+.s1
+Oil production does not depend on tech; you don't have to micro-manage
+to conserve oil.
+.s1
+Server time is in UTC, which means there will be no daylight savings
+time.
+.s1
+Missed updates due to server problems will be forced if caught within
+15 minutes of planned update time or skipped otherwise.
+.s1
+Everything you do in this game is logged by the deities for their own
+nefarious purposes.  However, the logs are treated confidentially.
+.s1
+Make the deity laugh and get up to 5 gold bars.
+.s1
+Source code and configuration is available from
+.br
+http://www.pond.sub.org/~armbru/empire/hvy-plastic-3/
+.s1
+.SA "Introduction, Server, show"

src/util/fairland.c

@@ -809,7 +809,7 @@ grow_islands(void)
 	secs = 0;
 	if (!place_island(c, &x, &y))
 	    return;
-	isiz = 1 + rnd(2 * is - 1);
+	isiz = 1 + rnd(is) + rnd(is);
 	do {
 	    ++secs;
 	    find_coast(c);
@@ -1080,6 +1080,7 @@ write_sects(void)
 		sct->sct_type = SCT_MOUNT;
 	    sct->sct_elev = total;
 	    sct->sct_newtype = sct->sct_type;
+	    sct->sct_dterr = own[sct->sct_x][y] + 1;
 	    if (ORE)
 		add_resources(sct);
 	}