Added encoded option and check_size to convert_imageset

Conflicts:
	tools/convert_imageset.cpp
Added encoded datum to io
Added test for encoded Datum to test_io.cpp
Added timers for benchmarking
Add fast code for transform(cv::Mat,Blob)
Add root_folder to ImageDataLayer
Speed up WindowDataLayer and add mean_values
Added cache_images to WindowDataLayer
Added root_folder to WindowDataLayer to locate images
Change caffe time to do forward/backward and accumulate time per layer
Upgrade compute_image_mean to use gflags, accept list_of_images, and print mean_values
Added CPUTimer
Make timing more precise using double and microseconds
Merge pull request #1239 from sguada/encoded

Allow using encoded images in Datum, LevelDB, LMDB