Fixed UI bug in distance, chroma, and difference nodes that caused the threshold to be limited by the falloff value. These should be independent. Cleaned up how falloff works in keying nodes.

Applied patch #23379. Does not change existing .blend files and looks
good.

Fixed bug in normalition of YCbCr color space conversion (from 0..1 to
-1..1) to fix errors in keying. Simplified chroma key to not take
despill into consideration (handled elsewhere). Simplified user
interface for pieces not used.

added capabilty to limit color spill by an input mask

oops forgot this!

Added a line sampler to the histogram panel in the image space.
Patch #21712 from Xavier Thomas.
now updates in real time as you pull the line.

added different sampling methods in rotate node
fixed bug in difference matte node that prevented using a solid color for second input
-also clairified some variable names to be more meaningful

added method to change algorithm used in channel matte node. Limit a channel by another channel or limit by max of remaining channels.

updated despill node to incorperate changes from Xavier Thomas's patch #18012

Added Levels Node (histogram, with mean/std deviation outputs)
Added RGB space distance matte Node
Added HSV color matte Node

Fixed Image difference matte Node to use image differences instead of RGB space distance
Fixed luminance node for low end values being read wrong
Fixed CMP_util copy/swap functions not accounting for all channels
Fixed UI for difference matte Node

Added RNA for new nodes