Issue #289. Disallow <= outside bloom blocks.

When used on scratches/interfaces, <= will have no effect outside a bloom block.
When used on tables, <= will place the tuples in, available in the *next* tick.

Disallowing <= loses us nothing that <+ doesn't provide, while also eliminating
a user-facing corner case.

Note that inside_budinit was added, because meta_rewrite calls BudCollection <=
during the rewrite phase. Otherwise, we just use inside_tick.

The error message looks like this:
../collections.rb:605:in `<=' : illegal use of <= outside of bloom block (Bud::CompileError)
        from XactKVSProtocol.rb:103:in `<main>'