phase: extract the phaseroots serialization in a dedicated method In most case, the file creation logic will be handled by the transaction itself. The write method has to stay around for the case where the repository is modified outside a transaction (strip).

transaction: add a file generation mechanism A new `transaction.addfilegenerator` function is added. It allows external code to register files to be generated. See inline documentation for details. It is important to gather all file creation logic on the transaction as at some point we'll want to mimic the "pre-transaction-commit" logic that we use for revlog. I'm refering to the logic that lets hooks see the result of the transaction before it actually gets committed.

transaction: backup file in a dedicated "namespace" File backup may conflict with other "journal.*" file. We add a fixed part in the backup name file to prevent it.

transaction: use `self.journal` to create backup file Transaction journal name is "journal" in most case, but it can be something else. We use the appropriate attribute to create the file.

memctx: add note about p2

memfilectx: add remove and write methods Similar to the previous patch for workingfilectx, this patch will allow abstracting localrepo.remove / write method to refactor working directory code but instead operate on files in memory.

workingfilectx: add remove and write methods This patch will allow abstracting localrepo.remove / write method to refactor working directory code.

memctx: create a filectxfn if it is not callable This will allow future patches to construct a memctx based on another context or any other store-type object.

test-patchbomb.t: work around Python change d579866d6419 (issue4188) Python 2.7.7 and later (as well as some ubuntu/debian packages of 2.7.6) include a fix that makes the email module more pedantically correct for MIME boundaries, but this breaks our tests. We work around this by filtering the output of any 'hg email' invocations in the test that produce MIME messages.

phase: add a transaction argument to retractboundary We now pass a transaction option to this phase movement function. The object is currently not used by the function, but it will be in the future. All call sites have been updated. Most call sites were already enclosed in a transaction for a long time. The handful of others have been recently updated in previous commit.