Jsonrpc error handlers can now safely call jsonrpc-shutdown

Jsonrpc error handlers can now safely call jsonrpc-shutdown

Previously, if an error handler called jsonrpc-shutdown, and if that
error handler was being called from the process sentinel,
jsonrpc-shutdown would infloop waiting for jsonrpc-sentinel-done to be
set.

Rename the process property jsonrpc-sentinel-done to
jsonrpc-sentinel-cleanup-started, arrange for it to be set earlier
in the sentinel, and also check for it earlier in jsonrpc-shutdown.

* lisp/jsonrpc.el (Version): Bump to 1.0.7.
(jsonrpc--process-sentinel): Set jsonrpc-sentinel-cleanup-started
a bit earlier than previous jsonrpc-sentinel-done.
(jsonrpc-shutdown): Query jsonrpc-sentinel-cleanup-started