Do not change bug numbers, these numbers are referred in Vlib/net.c

BUG1 (24.2.2003):
Cache for SP does not work properly. For examle:
   3------4
  /        \
 /          \
1------------2
If SP is called for 1->3 and then 1->4, the returned SP for 1->4 is 1,2,4
(which is longer than 1,3,4). If cache is not used or 1->4 is called first
result is OK (1,3,4). 
Note that even if cache is reset by application if 'from' is changed, SP is often incorrect.
So the problem is not if cache is reset, but how cache is used inside dglib.

BUG2 (24.2.2003):
If 2 nodes are connected by more arcs, SP doesn't return the shortest
one but the last arc (between these two nodes) inserted to graph.

WISH1 (24.2.2003): Use type 'double' for costs instead of 'integer'.