acu82141 cookbook caching
acu82141 cookbook caching fixes
acu82158 Add unit tests
acu82141 peer review feedback
acu82141 Use 'raise' instead of 'raise e' to preserve the original stack trace.
acu82141 safe cookbook tarball name generation
acu82158 keep specs green
Merge pull request #153 from rightscale/aqua_13_04_acu81697_cookbook_caching

RightLink skips downloading cookbooks that it already has