JxW neighbor in Assembly class has to come from the surface (closes #3345)

When integrating over the face surface, transformed jacobian weights
have to come from the surface.  It was incorrectly implemented and JxW
came from the volume. This also fixes the memory leak introduced by
copying a JxW array into another MooseArray.
Merge pull request #3349 from andrsd/neighbor-jxw

JxW in Assembly class has to come from the surface (closes #3345)