Use UTF-8 encoding by default when available.
extend the asdf contrib with an asdf system definition search function that finds swank, so that (asdf:load-op :swank) or dependence on it works as expected.
Added a restart to be able to skip loading swank modules.

Rationale: it helps when connecting to a server that has an older swank
than the connecting slime, or for some other reason the swank module is
not available.

Uses cl:continue, which can be controversial. Maybe it should use
something like swank::skip-require?
SBCL: use weak hashtables for thread accounting
Semantic noop.

Use 'continuation-id' name for more clarity around emacs-rex.