Fire late Monday night destroyed a Bucks County hotel. High winds and a frozen pond hampered firefighting efforts at the Oak Grove Country Inn, on Route 611 in the Pipersville Section of Bedminster Township.  They had to pump water from a pond about two miles away and take it to the fire scene in tanker trucks.  More than 15 guests escaped uninjured, thanks largely to hard-wired alarms that woke them up.  The cause was traced to an outdoor walkway behind the building, which had a bucket where cigarette butts were discarded.  A smoldering butt apparently ignited other butts, and the wind-fanned flames ignited the wooden walkway.  The fire has been ruled accidental.