Avoid cache of empty data. Improved CrawlPagedWeb search performer. Refactor of decrypter and common source code.
Split 'common/' into commit '7618c7b41375f0208e9a70fd5ca1de6be124f255'

git-subtree-dir: common
git-subtree-mainline: e28253a50bb3cf166b5b417308ba22ef4d1adeef
git-subtree-split: 7618c7b41375f0208e9a70fd5ca1de6be124f255