Include various checksum SchemeHandler, e.g. MD5, SHA1

[lefou]

To verify the checksum of a file, a Md5SumSchemHandler or a Sha1SchemeHandler might come in handy.

Example:

Target("phony:example") dependsOn "md5:3a7ac43fce6e9f9f0687c920c666f35e=http://sbuild.tototec.de/sbuild/attachments/download/88/de.tototec.sbuild-0.7.1.jar"

The target example depends on the file de.tototec.sbuild-0.7.1.jar which will be downloaded via HTTP and afterwards it's checksum is checked. The md5 scheme would fail, if the checksum of the downloaded file does not match.