Watershed fixes for issue #803

[LeeKamentsky]

This adds an ordering of the structuring elements that favors horizontal and vertical structuring elements over diagonal ones. I'd like this addition to be the fix for issue #803. The pull request was done on top of @kevin-keraudren's pull request #1520.

[JDWarner]

@blink1073 @arve0 we are now seeing this NumPy compilation failure on AppVeyor across several recent builds - e.g., here (#1530) and in #1483. At first I figured it was an intermittent issue, but it's looking more generalized.

If #1526 contains a solution, we should make squashing the last 2.7 bug and merging it a priority as this issue is holding up other PRs.

[arve0]

Not sure these errors are related to #1526, but adding windows wheels to a binstar channel (as mentioned by @jjhelmus) will most likely stabilize windows builds.

As of now, #1526 does not hold a complete solution, and I do not have time to finish it. So if its a pressing issue someone should pick it up.

[JDWarner]

@arve0 I think #1526 may have a solution, intended or accidental, for AppVeyor. I'm talking specifically about AppVeyor - I've seen this error in two PRs this weekend, but your last commit into #1526 built successfully on AppVeyor.

[JDWarner]

Hi @LeeKamentsky, could you rebase on master? There shouldn't be any conflicts, but the AppVeyor build is now fixed. Once we get the Windows green light we can merge this.

[JDWarner]

Lovely, AppVeyor times out on git clone.

Restart this one when you get the chance, @stefanv - I do not have the option on AppVeyor.

[jni]

Brilliant. Thank you again @kevin-keraudren and @LeeKamentsky for this fix and bonus enhancement! =)