some namespace simplification
Merge pull request #1269 from Yangqing/dev

Minor change: some namespace simplification
move registration code to corresponding cpp files.
Merge pull request #1270 from Yangqing/dev

Give back to layer what is layer's, and to factory what is factory's
Revert "OpenCV should be compiled using pkg-config options." -- breaks
compilation on working systems

This reverts commit 4587b2f9043996fed36fc989c00329ec829ecae9.
some namespace cleaning.
Merge pull request #1277 from Yangqing/dev

some more namespace cleaning.
fix layer factory