[Bf-codereview] Node socket selection reimplemented (issue 5727064)

[lukas.toenne at googlemail.com]

Ok, this is a bit tricky due to keymap inconsistency
(SELECTMOUSE/ACTIONMOUSE for select, LEFTMOUSE for link) and the need
for operator pass-through, but i think i have a nice solution. Problem
is that in order to get to the link operator the selection always has to
return pass-through, but if socket select does that then the node select
op will deselect all previous nodes and sockets again ...

What i did now is merge the socket selection operators into the existing
node select operator (sockets checked first, then nodes). This way the
socket/node blocking from overlap can be done completely internal in the
operator, which is also nicer because sockets are part of nodes after
all.

Also sockets only get deselected when the link operator is successful
(not on cancel), so left click can still be used for socket select too.

The autoconnect operator could still use some tweaking to make it more
reliable, but i'd rather do that in a separate patch later. Tests look
good, so will commit this to trunk today.

http://codereview.appspot.com/5727064/