symlog scale no longer shows labels on the negative side

[anntzer]

Compare
http://matplotlib.org/devdocs/examples/scales/scales.html (~2.0b4)
and
http://matplotlib.org/examples/scales/scales.html (1.5.3)
no tick labels are drawn on the negative side of the symlog plot in 2.0b4, unlike e.g. 1.5.3 which works fine.
Bisected back to PR #5161, but some commits within the PR don't run so I can't do better.

[egaudry]

might be linked to #7202

[NelleV]

Code to reproduce the bug:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import colors
from matplotlib import ticker

X = -1 * np.random.randint(10, 90, size=(100, 100))

fig, ax = plt.subplots()
m = ax.imshow(X, norm=colors.SymLogNorm(1))
formatter = ticker.LogFormatter(10)
cb = fig.colorbar(m, format=formatter)
ax.set_title("label only base")

[NelleV]

That was on the wrong ticket…