It took Portland firefighters nearly four hours to rescue a woman who was trapped between the walls of two buildings Wednesday morning. She apparently fell from a two story rooftop.  She was wedged in an 18-inch space.  Fire Bureau Lt. Rich Chapman says she couldn't move, and they had to use concrete cutting saws to open holes in a cinderblock wall.  With temperatures near freezing, heaters were used to blow warm air into the space.  The woman was covered with lubricant to help her slide free.  She was taken to a hospital for evaluation.