[pstricks] Extension of \psGetSlope to accept more general coordinate inputs...

[Werner Grundlingh]

At the moment, \psGetSlope in the pstricks-add package requires the
following specification:
  \psGetSlope(#1,#2)(#3,#4)#5 % \psGetSlope(x1,y1)(x2,y2)\<macro>

Would it be possible to extend this format to that of the other
pstricks macros such that the following examples would also work:
  \psGetSlope(3;30)(4;65)\SlopeVal
  \psGetSlope([offset=3pt]1,0|0,2)([nodesep=10pt,angle=30]5,2|othernode)\SlopeVal

Werner