This reduces memory cost somewhat (10MB on the git.git repository),
while still keeping the same functionality :) Better would be to
use structs in a c array in the cellinfo, as the NSArray and
NSObject type information together now use more memory.
This introduces a new object, PBGitLane that keeps track of the current lane.
We used to only need a sha for a lane, but now that more information is
needed, an extra object is in order. PBGitLane keeps a lane index number. This
number is later used to pick a color.
Pieter de Bie