Update OpenCollar - leash.lsl

this tries to fix part of the problems in #342 
the test line 789: iDist<1.2*g_iLength+10)
compares distance between wearer and leasher with a treshold distance that depends on the leash length.
So there are 3 zones
- under the leashlength : the leash is not taut and the wearer  is "free"
- over the leashlength : the leash is taut and the wearer  is pulled
- further (new) : the situation is abnormal and the leash is disabled until the leasher comes back close enough.