remove prohibition on `handle-evt?' arguments to `wrap-evt', etc.

The intent of disallowing `handle-evt?' arguments to `wrap-evt',
`handle-evt', and `chaperone-evt' was that those extra wrappers
break the tail-handling behavior that is almost certainly intended
when `handle-evt' is used. The extra checking was not obviously
worthwhile (we don't have any checked "this procedure should be called
in tail position" annotations, after all), and pushing the distinction
through Typed Racket looked particularly inconvenient.

Dropping the constraint is trivial if we say that wrapping a
`handle-evt' result disables the tail invocation of the handler
procedure.
Revert "make user PLaneT install path use installation name instead of version"

This reverts commit ac20e7fc0d0e60874cc0b47e5d15727e412f5500.

Using the installation name name seems right, but it creates sandbox
trouble, since finding the instalation name requires several
path-chasing steps. I think the sandbox problem shoudl be fixed,
somehow, but since I don't have a good idea right now, I'm reverting
the PLaneT change.