Cairo backend ignores alpha in imshow. - #1193

import matplotlib
matplotlib.use('cairo')
import numpy as np
import matplotlib.pyplot as plt

z = np.arange(150)
z.shape = (10,15)

fig, axs = plt.subplots(1,1)

ax = axs
im = ax.imshow(z, interpolation='nearest', alpha=0.3)
cbar = fig.colorbar(im, ax=ax)

plt.savefig("test2.png")
plt.savefig("test2.pdf")
plt.savefig("test2.svg")
plt.show()