clabel can be called with approximate postions of labels

[leejjoon]

This is to address #613.

With this patch, clabel can take a list of positions and contour labels will be created near those positions.
For example,

plt.figure()
CS = plt.contour(X, Y, Z)
manual_locations = [(-1, -1.4), (-0.62, -0.7), (-2, 0.5), (1.7, 1.2), (2.0, 1.4), (2.4, 1.7)]
plt.clabel(CS, inline=1, fontsize=10, manual=manual_locations)

The positions should be in data coordinate.

[efiring]

Why is this commented out block still here? Did you forget to delete it?
You could use this construct; master is 2.6 and up now, so if it requires 2.5 and up, it is OK.
I think that using it inside a long argument list like this is bad for readability, though.

[leejjoon]

This was my oversight. I was simply refactoring related code and didn't take a careful look.
I'll fix it and merge it to master.