Communication between comet actor and snippet via RequestVar

[fixundfertig123]

There are use cases when one wants to hand over params from CometActor to snippets via RequestVars. One example would be a SHtml.link() within a CometActor where the parameter could be passed by a RequestVar snapshot.

This issue is discussed in https://groups.google.com/forum/#!topic/liftweb/N_yNYnaErhQ

[Shadowfiend]

The snippet refactor I want to work on for, amongst other things, #1799, may provide some better approaches here. We're dealing with some of these issues at work and have come up with a few interesting ways to try to deal with it.