Fix: issue 965 speed up clusters extraction

Use patch provided Marvin Gordon to speed up clusters extraction in the loop.
Replce the copy part by a proper constructor improved further the performances.
Update: renice console outputs

Replace std::cout with proper pcl::console::print_*
Add watch to get extraction time
Provide an optional switch "-dump" to write out extracted clusters to "clusters.dat"
Fix: indentation and coding style
Merge pull request #30 from nizar-sallem/master

Bug #965