Fix warnings in io/ply_io.h

> ply_io.h:524:29: warning: private field 'vertex_properties_counter_' is not used [-Wunused-private-field]
Fix warnings in io/ascii_io.cpp

> ascii_io.cpp:109:21: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
> ascii_io.cpp:165:24: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
Fix warnings in io/lzf_image_io.cpp

> lzf_image_io.cpp:243:21: warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]
Fix warnings in io/lzf_image_io.hpp

> lzf_image_io.hpp:329:24: warning: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'int' [-Wsign-compare]
Fix warnings in io/ifs_io.cpp

> ifs_io.cpp:65:7: warning: unused variable 'specified_channel_count' [-Wunused-variable]
> ifs_io.cpp:190:16: warning: unused variable 'nr_points' [-Wunused-variable]
> ifs_io.cpp:244:16: warning: unused variable 'nr_points' [-Wunused-variable]
Fix warnings in io/lzf_image_io.hpp

> lzf_image_io.hpp:82:21: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> lzf_image_io.hpp:84:32: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
Fix warnings in io/robot_eye_grabber.cpp

> robot_eye_grabber.cpp:169:21: warning: comparison of integers of different signs: 'int' and 'const size_t' (aka 'const unsigned long') [-Wsign-compare]
Fix warnings in io/dinast_grabber.cpp

> dinast_grabber.cpp:280:44: warning: comparison of integers of different signs: 'size_type' (aka 'unsigned long') and 'int' [-Wsign-compare]
> dinast_grabber.cpp:292:42: warning: comparison of integers of different signs: 'size_type' (aka 'unsigned long') and 'int' [-Wsign-compare]
> dinast_grabber.cpp:310:21: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> dinast_grabber.cpp:312:23: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> dinast_grabber.cpp:415:25: warning: comparison of integers of different signs: 'size_type' (aka 'unsigned long') and 'int' [-Wsign-compare]
Fix warnings in io/libpng_wrapper.cpp

> libpng_wrapper.cpp:245:21: warning: comparison of integers of different signs: 'int' and 'png_uint_32' (aka 'unsigned long') [-Wsign-compare]
Fix warnings in 2d/edge.hpp

> edge.hpp:219:28: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> edge.hpp:485:13: warning: unused variable 'height' [-Wunused-variable]
> edge.hpp:486:13: warning: unused variable 'width' [-Wunused-variable]
Fix warnings in features/organized_edge_detection.hpp

> organized_edge_detection.hpp:263:24: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> organized_edge_detection.hpp:265:26: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> /organized_edge_detection.hpp:306:24: warning: comparison of integers of different signs: 'int' and 'const uint32_t' (aka 'const unsigned int') [-Wsign-compare]
> organized_edge_detection.hpp:308:26: warning: comparison of integers of different signs: 'int' and 'const uint32_t' (aka 'const unsigned int') [-Wsign-compare]
> organized_edge_detection.hpp:321:24: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
> organized_edge_detection.hpp:323:26: warning: comparison of integers of different signs: 'int' and 'uint32_t' (aka 'unsigned int') [-Wsign-compare]
Fix warnings in 2d/kernel.hpp

> kernel.hpp:172:21: warning: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Wsign-compare]
> kernel.hpp:143:21: warning: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Wsign-compare]
Fix warnings in features/esf.hpp

> esf.hpp:77:9: warning: unused variable 'h_d1' [-Wunused-variable]
Fix warnings in keypoints/narf_keypoint.cpp

> narf_keypoint.cpp:144:3: warning: unused function 'translateDirection180To360' [-Wunused-function]
> narf_keypoint.cpp:161:3: warning: unused function 'translateDirection360To180' [-Wunused-function]
> narf_keypoint.cpp:173:3: warning: unused function 'nkdGetDirectionVector' [-Wunused-function]
Fix warnings in keypoints/agast_2d.cpp

> agast_2d.cpp:263:23: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
> agast_2d.cpp:291:23: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
Fix warnings in visualization/pcl_visualizer.hpp

> pcl_visualizer.hpp:940:24: warning: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'int' [-Wsign-compare]
Fix warnings in visualization/histogram_visualizer.hpp

> histogram_visualizer.hpp:117:21: warning: comparison of integers of different signs: 'int' and 'pcl::uint32_t' (aka 'unsigned int') [-Wsign-compare]
> histogram_visualizer.hpp:203:21: warning: comparison of integers of different signs: 'int' and 'pcl::uint32_t' (aka 'unsigned int') [-Wsign-compare]
Fix warnings in visualization/image_viewer.hpp

> image_viewer.hpp:391:18: warning: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'int' [-Wsign-compare]
Fix warnings in visualization/pcl_plotter.cpp

> pcl_plotter.cpp:567:21: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
> pcl_plotter.cpp:584:21: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]
Merge pull request #446 from taketwo/fix-warnings

Fix compiler warnings