Created by: tschaub
While the gulp-changed and gulp-cached plugins work great with 1:1 src:dest file mapping, they should not be used for n:1 src:dest mapping. With plugins like gulp-concat, css-sprite, etc. that generate a single output file given many input files, you want to compare the modification time of the output file to the modification file of each input file (and use all if any are newer).
The gulp-newer plugin works with both 1:1 and n:1 src:dest mapping by comparing mtime.