Blender Git Loki

Reimplemented the earlier feature of swapping existing links to
neighboring sockets when connecting to an occupied input.

This now works based on socket names rather than types, which helps to
avoid unwanted connections to arbitrary sockets. Sockets are considered
swappable when their names match, based on an alphabetic prefix followed
by non-alphabetic suffix.

For example:
Image - Image : matches
Color1 - Color2 : matches (used e.g. in cycles mix nodes)
Roughness - Rotation : does not match (suffix is still alphabetic)