arogue5: fix the crash when checking prices in shops.

A buffer called curpurch, which stores a description of an item in a
trading post which the player might be interested in, was only 15
bytes.  It was overflowing into oldrp, a room pointer, leading to
segfaults.  The size of curpurch has been increased to LINELEN*2,
which matches the size of prbuf, which is returned by inv_name and
then strcpy()'d to curpurch.  As long as nothing overflows prbuf it
should be safe now.

NOTE that this breaks savefile compatibility.

arogue5/rogue.c

@@ -65,7 +65,7 @@ int spell_power = 0;
 int turns = 0;				/* Number of turns player has taken */
 int quest_item = 0;			/* Item player is looking for */
 char nfloors = -1;			/* Number of floors in this dungeon */
-char curpurch[15];			/* name of item ready to buy */
+char curpurch[LINELEN*2];		/* name of item ready to buy */
 char PLAYER = VPLAYER;			/* what the player looks like */
 char take;				/* Thing the rogue is taking */
 char prbuf[LINELEN*2];			/* Buffer for sprintfs */