slightly better handling of read errors in the debugger

wrap the read as well as the eval in the WITH-SIMPLE-RESTART ABORT
so that the user can return to the existing debugger level on read
errors.
Don't go through fdefn when referencing #'known-functions.

Known functions are know to be always present, save on indirection by
using them directly.
Make %coerce-callable-to-fun static on x86oids.

It's called a lot when doing funcall or apply.
Avoid consing in SLEEP.

Try to compute seconds without consing, when the arguments are small
enough (in the fixnum range).

Add a transform to go directly to sb-unix:nanosleep when possible.