Encode string to md5 hex value.

source: https://github.com/gogits/gogs/blob/9ee80e3e5426821f03a4e99fad34418f5c736413/modules/base/tool.go#L58.

http://code.google.com/p/go/source/browse/pbkdf2/pbkdf2.go?repo=crypto.

Walk walks a path, optionally following symbolic links, and for each path,it calls the walkFn passed.

WalkSkipDir is the Error returned when we want to skip descending into a directory.

WalkFunc is a callback function called for each path as a directory is walkedIf resolvedPath != "", then we are following symbolic links.