test-compat: merge with mercurial-4.2

test-compat: merge mercurial-4.2 with the new stable branch content

branching: default into stable It is time for a new release

compat: handle pre-4.2 compatibility for accessing vfs The vfs module is quite new.

compat: avoid using configoveride This not supported before mercurial 4.1.

compat: use old style method to update bookmark The '_del' and '_set' method are new additions in 4.3 we should not use them in the compatibility layers.

topic: wrap 'update' in a more flexible way This ensure compatibility with mercurial 4.1 and below

branching: open the mercurial 4.2 compatibility branch The freeze as started.

readme: add an entry about the unified message

touch: use precheck to validate revision This gives us standard check and standard error message.

prune: use precheck to validate revision This gives us standard check and standard error message.

uncommit: use precheck to validate revision This gives us standard check and standard error message.

amend: use precheck to validate revision This gives us standard check and standard error message.

split: use precheck to validate revision This gives us standard check and standard error message.

precheck: handle rewrite attempt of nullrev This is a common breaking case, so we handle and test it in the generic code.

precheck: update the orphan message to something me generic This will help to reuse it for other commands.

precheck: point to the instability doc when aborting This will help user to understand what is going on.

evolve: document the various instability/troubles We need something to point people at.

precheck: also check for unstability creation

prefetc: point at the offending changeset when aborting We do our best to display comptact but usable information.

precheck: point to 'phase' help when aborting some of the error message already does that. It seems a good idea.

precheck: use 'changesets' in the message instead of 'revisions' This match the message `hg commit --amend` issue in core.

rewriteutil: add a precheck function to validate rewrite beforehand For now this only checks for changeset mutability and this is only used by 'checkfold'. We'll expand the checking and usage as we go.

test: remove reference to the graphlog extension The feature is in core for ages.

test: use common setup for test-split.t This make things cleaner.

split: compute revision to split after locking This would avoid strange behavior from race condition.

split: basic code cleanup We remove a useless extra variable since another one already hold the same value.

commands: rewrite the 'evocommands' module to 'cmdrewrite' The remaining commands should get their own module, so we rename the module for clarity. We update the module comments to better fits its purpose.