[Bf-python] Ipo/IpoCurve API revisited

[Ken Hughes]

I was looking through the curve documentation today and was reminded how 
I continue to be annoyed with the Ipo/Ipocurve API, particularly:
* Ipo and Ipocurves don't allow the [] operator to access curves and points,
* no good way for the user to detect which Ipo curve names are valid 
with which Ipo, and
* the inability to access material texture channels other than channel 0

I decided to play around some today, and implemented mapping methods 
(read-only).  Makes it possible to do "ipo['LocX']" or "ipo[Ipo.LocX]"; 
throws a Key Error exception if the curve isn't defined (either because 
the Ipo doesn't support that key or because it hasn't been created for 
this Ipo; could also throw a Value Error to differentiate).  I also 
added an attribute which lets you get the valid curve names for the 
particular type of Ipo; so "names = ipo.curveNames" gives a list of the 
valid names which can then be used.  A generator could also be added to 
let you iterate over the active curves, I suppose.  Plus, later add 
assignment/creation of curves by "ipo['LocX'] = IpoCurve.New()" or 
something.

The [] operator for Ipocurves should be a no-brainer; it should be even 
simpler than CurNurb since there are no NURBS in IPOs.

The material texture channel stuff.... well, I figured out something for 
this last summer but got lost in the patch tracker.  Will revisit that 
problem later.

Anyway, what are people's thoughts?  It's not something for 2.40, but 
maybe the Orange people would like to try it out.

Ken