mdiff.unidiff: add support for noprefix

diff: add a --noprefix option See previous patch descriptions for the motivation. The tests reflect the current state of the world -- as we add support we'll see changes in the test output.

patch.diffopts: add support for noprefix In an upcoming patch we'll enable support as an option to 'hg diff' as well. The tests reflect the current state of the world -- as we add support we'll see changes in the test output.

patch.diffopts: allow a setting to be forced in plain mode Upcoming patches will add an option that will almost certainly break diff output parsers when enabled. Add support for forcing an option to something in plain mode, as a fallback. Options passed in via the CLI are not affected, though -- it is assumed that any script passing the option in explicitly knows what it is doing.

patch.diffopts: break get function into if statements We're going to add another condition here, and with the current structure that becomes just too confusing.

mdiff.diffopts: add a new noprefix option By popular demand, we introduce an option to disable the 'a/' and 'b/' prefixes in diff output. This makes copying and pasting filenames from diff output easier. This option will be implemented and documented in upcoming patches. To ensure that existing scripts that parse output don't break, we will ensure that this prefix is disabled in plain mode. A straight 'hg export | hg import' without HGPLAIN=1 will still be broken though, but there's little that can be done about that.

mdiff.diffopts: add doc comment for nobinary

changelog: register changelog.i.a as a temporary file The file is registered to make sure the transaction is cleaned up in all cases.

transaction: allow registering a temporary transaction file During the transaction, files may be created to store or expose data involved in the transaction (eg: changelog index data are written in a 'changelog.i.a' for hooks). But we do not have an official way to record such file creation and make sure they are cleaned up. The lack of clean-up is currently okay because there is a single file involved and a single producer/consumer. However, as we want to expose more data (bookmarks, phases, obsmarker) we need something more solid. The 'backupentries' mechanism could handle that. Temporary files can be encoded as a backup of nothing '('', <temporarypath>)'. We "need" to attach it to the same mechanism as we use to be able to use temporary transaction files outside of .'store/' and 'backupentries' is expected to gain such feature. This changeset makes it clear that we should rename 'backupentries' to something more generic.

transaction: always generate file on close The conditionnal was buggy and file were only generated if "onclose" was defined. By luck, "onclose" was always defined.