evolve: move builddependencies() and _singlesuccessor() to utility module The builddependencies() and _singlesuccessor() function are very useful functions and can be used at a lot of places. They are also used in topic extension also, so let's move them to utility. However moving them to utility won't help anything in the topic extension.

utility: move MultipleSuccessorsError from __init__.py The MultipleSuccessorsError is required in multiple modules in upcoming patches, so let's move it to utility first.

evolvecmd: move more core from __init__.py to evolvecmd.py We are done with moving helper code, we will now be moving the evolve command in the new module.

evolvecmd: move code from __init__.py to evolvecmd.py

evolvecmd: move more code from __init__.py to evolvecmd.py We are now very close to have most of the evolve related code in evolvecmd.py.

evolvecmd: move more chunks of code from __init__.py to evolvecmd.py

evolvecmd: move more functions from __init__.py to evolvecmd.py If things are looking ugly, hold on.

evolvecmd: introduce a new module to handle `hg evolve` related code __init__.py is to cluttered with wrapping and all, it's better to move code related to evolve command to new a module which will help us in great refactoring and introducing nice and better flow of data through functions. There is a temporary import cycle is introduced which will be fixed in the series.

evolve: remove not required calls to phases.retractboundary() To make sure phases are preserved during evolve, we started using the phases.new-commit config option. Now we don't need to call phases.retractboundary(). Let's remove the redundant code.

evolve: store the replacements occurred during `hg evolve` at top level This patch starts storing the replacements made during the `hg evolve` command. The current dictionary is not used anywhere but will be used in future as we want to introduce abort functionality, so we want to delay writing of obsmarkers, storing these exchanges in statefile etc.