add tools to work with mercurial repositories

Resolves:

    $ go get github.com/rakyll/drive
    go: missing Mercurial command. See http://golang.org/s/gogetcmd
    package code.google.com/p/goauth2/oauth: exec: "hg": executable file not found in $PATH
update all packages in base image at build-time
add host and dig commands to devenv
add ftp and tftp clients

These are useful for testing other services.
use the "semi-official" fedora 20 base image