gitweb.cgi: Include direct link to "raw" files from "history"

In "history" view, the "page_path" is now also a URL link to
the "raw" format of the file, which will always give you
the latest version in the repository.

This is helpful for externally linking files, such that
the latest version is always referenced and in "raw" format.

Signed-off-by: Luben Tuikov <redacted>
Signed-off-by: Junio C Hamano <redacted>