- intersect returns parameter tuples

- intersect returns parameter tuples
- removed range checks for parameters
- intersect only returns intersection points which are farther than epsilon apart
  (closed paths still have to be done)
- subnormpath checks and remembers short segments
- added close method to subnormpath
- renamed: normpathitem -> subnormpathitem
- added modified method to subnormpathitem, which returns a new subnormpathitem with changed
  start and end point
- arrowhead generation has been cleaned up

git-svn-id: https://pyx.svn.sourceforge.net/svnroot/pyx/trunk/pyx@1820 069f4177-920e-0410-937b-c2a4a81bcd90