getchangegroup: take an 'outgoing' object as argument (API) There is various version of this function that differ mostly by the way they define the bundled set. The flexibility is now available in the outgoing object itself so we move the complexity into the caller themself. This will allow use to remove a good share of the similar function to obtains a changegroup in the 'changegroup.py' module. An important side effect is that we stop calling 'computeoutgoing' in 'getchangegroup'. This is fine as code that needs such argument processing is actually going through the 'exchange' module which already all this function itself.

outgoing: add a 'missingroots' argument This argument can be used instead of 'commonheads' to determine the 'outgoing' set. We remove the outgoingbetween function as its role can now be handled by 'outgoing' itself. I've thought of using an external function instead of making the constructor more complicated. However, there is low hanging fruit to improve the current code flow by storing some side products of the processing of 'missingroots'. So in my opinion it make senses to add all this to the class.

outgoing: adds some default value for argument We are about to introduce a third option to create an outgoing object: 'missingroots'. This argument will be mutually exclusive with 'commonheads' so we implement some default value handling in preparation. This will also help use to make more use of outgoing creation around the code base.

outgoing: pass a repo object to the constructor We are to introduce more code constructing such object in the code base. It will be more convenient to pass a repository object, all current users already operate at the repository level anyway. More changes to the contructor argument are coming in later changeset.

match: remove matchessubrepo method (API) Since it is no more used in cmdutil.{files,remove} and scmutil.addremove we remove this method.

subrepo: cleanup of subrepo filematcher logic Previously in the worst case we iterated the files in matcher twice and had a method only for this, which reimplemented logic in subdirmatchers constructor. So we replaced the method with a subdirmatcher.files() call.

pycompat: delay loading modules registered to stub Replacement _pycompatstub designed to be compatible with our demandimporter. try-except is replaced by version comparison because ImportError will no longer be raised immediately.