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.
