* module/language/cps/intmap.scm (intmap->alist, print-intmap)
(print-transient-intmap): New functions.
Install the new functions as printers for <intmap> and <transient-intmap>.
* module/language/cps/intmap.scm (make-atomic-reference):
(get-atomic-reference, set-atomic-reference!): New helpers.
(*branch-size-with-edit*, *edit-index*): Branches now have a trailing
field, an atomic reference to their owner.
(<transient-intmap>): New record type. A mutable intmap.
(new-branch): Set the "edit" field on the branch.
(clone-branch-and-set): No editor for this field.
(assert-readable!, writable-branch): New helpers.
(transient-intmap, persistent-intmap): New exported functions.
(intmap-add!): New function.
(intmap-next, intmap-prev, intmap-ref): Work on transient intmaps.
(intmap-fold): Persist the intmap before folding over it.
* module/language/cps/intmap.scm (*branch-bits*): Switch to 32-way
branching. Marginally faster on lookup, and creation costs can be
amortized via using the transient interface. Marginal speedup for
assembler.scm compilation.
* module/language/cps/intmap.scm (meet-error): New helper.
(intmap-add, intmap-union, intmap-intersect): The "meet" argument is
optional and defaults to meet-error.
