Raft Separation Distance : Allow Negative numbers

[joeB1]

While printing with multiple materials, there are times when i need to use Material A for the raft and Material B for the support.
In that case i need to really have my support bite into the raft. I DON'T want them to separate.

Even when the Separation Distance is set to ZERO it still adds an offset in the gcode. It can be seen in the preview as well.
This makes HIPS curl off of the raft and ruins prints.

If i can tune this to a negative number it will prevent a lot of hand hacking of the gcode.

[austinreid]

I second this. Allowing more flexibility in tuning the separation distance is crucial for multiple-material prints.