A few tweaks, and the removal of an issue.
The perceived issue was a lack of GC on hashes containing closures. Turned out the closures were
references back to the hash itself, causing a cycle, which needs to be dealt with by cycle detection.
Version bump to 2.26
Automatic cycle detection every autogc instructions, where autogc is a
property (and so can be read/set with ?autogc and !autogc).
Default GC cycle detect interval now 100000 instructions