changing Path1 to SpannedIdent everywhere

Per an excellent suggestion from @acrichto, I'm using the (existing)
SpannedIdent rather than the unneccessary Path1. I'm leaving this as
a separate commit just to have some record of the history; when reviewing
this, I advise just reviewing the net change rather than the commit-by-
commit history.
DONT LET THIS COMMIT GO UPSTREAM
simplify and uncomment lambda-var hygiene unit test
comments only
comments only
WIP hygiene for itemfns
remove vestigial parsing of 1 .. id