Connected-component labeling

Connected-component labeling with 8-connectivity.

This function is partly based on the two-pass algorithm, described here:

http://en.wikipedia.org/wiki/Connected-component_labeling

I did not make use of the disjoint data set structure (at least that I am aware of) to connect the linked labels.

The same functionality is available in the image processing toolbox as the function bwlabel, but this function can be useful for those who want to study the implementation of the algorithm, or those who do not have access to the toolbox.