fix "alpha" kwarg in errorbar plot

- this patch was rightly proposed by Hans Dembinski on the matplotlib
  devel mailing list but never incorporated it seems
changing errorbar test to cover "alpha" kwarg
Merge pull request #1675 from megies/errorbar_alpha

fix "alpha" kwarg in errorbar plot
Fix overwriting suptitle
Add suptitle overwrite test
Update test_pickle baseline image
Merge pull request #1663 from dmcdougall/fix_suptitle

Fix suptitle
Merge branch 'v1.2.x'

Conflicts:
	lib/matplotlib/tests/baseline_images/test_axes/errorbar_mixed.pdf
	lib/matplotlib/tests/baseline_images/test_axes/errorbar_mixed.png