Use valid MathJax delimiters.

MathJax does not support $ as a delimiter by default, so math was not
displayed properly on the “Forward and Backward” page.
Fix minor typos in strings.
Merge pull request #1607 from kjkjava/master

Use valid MathJax delimiters.
Merge branch 'master' of https://github.com/BVLC/caffe into mobile
added pre-generated protobuf .h & .cc
added mkdtemp.h for NDK compatibility
added mobile test scripts