Add class check when setting n_init inside K-modes constructor

[DTchebotarev]

Currently, when creating a KPrototypes instance, there's a misleading message, which says that n_init is 1, when it's actually not:

This occurs because n_init is actually being set twice: once within KPrototypes.__init__() and once again within KModes.__init__() as a result of the super(KPrototypes, self).__init__(...) call.

I'm adding a check within the KModes.__init__() method that actually checks that it's being called from KModes, and only do the n_init logic in that case. Now, the "Initialization method and algorithm are deterministic. Setting n_init to 1." is only printed when initializing K-modes with the Cao init, but suppressed when initializing K-prototypes.

[coveralls]

Coverage: 97.942% (+0.009%) from 97.934% when pulling 41253f6 on DTchebotarev:master into 2d06e3c on nicodv:master.

[nicodv]

LGTM

[nicodv]

Thanks for the contribution, @DTchebotarev !

Coming back to this code some time after I wrote it, I think an even better solution is to not make KPrototypes inherit from KModes. But that's a fix for another day.