release: Finish preparation for 4.8.0

release: Merge default into stable for release preparation

default.nix:updated format to be consistent with CE package

svn: implemented svn verify function. - allows to check SVN version compatability.

logs: improve message.

hooks: expose pushed refs inside hooks. - we'll use pushed refs for Branch permissions - pushed refs will also be used to expose quick links to open pull request.

hooks: fixed function signature.

hooks: expose post-key-push hook for Mercurial.

hooks: show git stderr when git hook execution fails. - help with debugging.

evolve: expose hidden and obsolete flags for Mercurial repositories.