Quiverkey() positions arrow incorrectly with labelpos 'N' or 'S' #5613
Description
The documentation for quiverkey() in versions 1.3 through 1.5 states that
If labelpos is 'N' or 'S', X, Y give the position of the middle of the key arrow.
This guarantee is clearly violated in version 1.5:
The script that generated these figures is
import numpy
import matplotlib
from matplotlib import pyplot
plot = pyplot.quiver(*numpy.random.rand(2, 10, 10))
pyplot.xlim(-2, 12)
pyplot.ylim(-2, 12)
pyplot.quiverkey(plot, 0.5, 1, 1, 'N', labelpos='N')
pyplot.quiverkey(plot, 1, 0.5, 1, 'E', labelpos='E')
pyplot.quiverkey(plot, 0.5, 0, 1, 'S', labelpos='S')
pyplot.quiverkey(plot, 0, 0.5, 1, 'W', labelpos='W')
pyplot.annotate(matplotlib.__version__, (0, 0), (-1, 11), 'data', 'data',
ha='left')
pyplot.savefig('quiver_{}.png'.format(matplotlib.__version__))