ENH: Add some more coverage for MultiThreshold

Add the convenience methods.
Skip code on win32 that involves NaN.

Change-Id: I4406ff0ca66842d1a32ddfcc2983810d3eedf3eb
Fix double to unsigned char cast error on clang compiler.

Change-Id: I3979f3eeb2407a9924e57cf4b8540ea67693807e
Merge topic 'FixBoxPlot_doublecast' into master

35261130 Fix double to unsigned char cast error on clang compiler.
Merge topic 'Improvements_UnitTestMultiThreshold' into master

6cb7f089 ENH: Add some more coverage for MultiThreshold