histedit: use parse-error exception for parsing

test-histedit-edit: test histedit with dirty repo

histedit: limit mentioning histedit-last-edit.txt Before histedit-last-edit.txt would be mentioned for any failure. After, it should only be mentioned for failures relating to user input.

histedit: check fold of public change during verify

histedit: pass previous action to verify

annotate: mention that -n is suppressed in help

test-bundle2-format: force gc so a GeneratorExit will be thrown PyPy has looser semantics than CPython for when a generator's close method will be called. Forcing the gc causes it to be called at the right moment.

test-bad-extension: account for PyPy/CPython error difference

demandimport: update obsolete comment

demandimport: add support for PyPy PyPy's implementation of __import__ differs subtly from that of CPython. If invoked without a name or fromlist, it throws an ImportError, whereas CPython returns a reference to the level-appropriate importing package. Here, we achieve the same behaviour by hand.