Minor code cleanup.
Don't use monotone whitelist to detect unsafe function calls.

There has long been a conflation between "unsafe functions" (i.e., global
functions or Bud instance methods whose value might change between ticks) and
"monotone functions", which have the normal Bloom^L meaning. This has always
been wrong. Hence, stop using the monotone whitelist to identify safe functions;
instead, move the list of safe functions to a separate whitelist.
Tweak: replace two more uses of "+=" on collections.

This can have surprising semantics and is slow anyway; see
532a094f309b9861694f80cfa0a71b4d458e8b4b and related commits.
Trivial code cleanup for notin.
Fix #291: bug in rescan logic for notin operator.

The previous coding reset the notin operator's state (in particular, the hash
tables it keeps that hold copies of its input relations) unconditionally. That
is incorrect: if one of the inputs is not in rescan mode (e.g., because it is a
persistent collection), the content of that hash table will not be recreated in
the subsequent tick, which would result in emitting incorrect output. The proper
fix is to use the same logic that the join operator does: only discard hash
tables corresponding to input relations that are marked for rescan.
Update release notes.
Fix error when output of notin sent to a lattice identifier.

The code that routed output tuples for "notin" was never updated to account for
the possibility that the output collection might be a lattice. As it turns out,
there is no reason for notin to use its own implementation of this code; simply
deleting it and relying on the parent-class push_out() implementation fixes the
problem and removes some redundant code at the same time.
Improve error reporting for notin.

Previous coding to report an error upon an unknown column name in the notin
predicate list was just wrong.
Improve error message reporting.

When including the source for the relevant rule, report the source before
attribute name => number rewrite, not after.
Minor tweaks for notin docs.
Minor code cleanup for notin.
Improve notin test case.
Minor tweak for notin code.

Replace map for column lookup with values_at.
Add sanity check to notin code.
Merge branch 'master' of github.com:bloom-lang/bud