This makes the PBGitRevisionCell a bit nicer by retrieving all values
from the PBGitCommit object itself, and using another NSTextFieldCell to
draw the text.
This mean that PBGitGrapher now stores its information in the PBGitCommit's,
rather than in a custom grapher array. Also, because we don't need the
grapher to display refs anymore, the ref labels are also displayed when
using path limiting (for example, 'gitx -- Makefile').
This uses the C fgets() over the weird readLine implementation I found.
It speeds up the rev-parsing significantly: we went from ~4.5 seconds
on the git.git repo to ~0.95 seconds. And that's with the secret new date
parsing!
Pieter de Bie