Fix some issues in htools apidoc generation

First, auto-generated files were not processed if HsColour thus the
'source' link in Haddock documentation was dangling.

Second, we document the original Python constant name in the
Ganeti.Constants source, so that it's easily retrievable (as opposed
to undoing the name transformation).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>