Revision 1067

Added dvipng subroutine.  Corrected some errors in math2image.  dvipng
is still not being called correctly -- I think math2image needs more
updates.

dvipng is also in IO.pm, but making this available to WeBWorK1.8 seems
like a lot of work, hence I've only made a copy of the dvipng subroutine
from IO.pm.  With luck this will not interfere with WeBWork2.0.  I'm
open to suggestions for a better way to make both dvipng methods
available to both WeBWorK2.0 and WeBWorK 1.8
--Mike