copies: refactor checkcopies() into a top level method This moves checkcopies() out of mergecopies() and makes it a top level function in the copies module. This allows extensions to override it. For example, I'm developing a filelog replacement that doesn't have rev numbers so all the rev number dependent implementation here needs to be replaced by the extension. No logic is changed in this commit.

store: move top file walk to a separate function Some extensions find it useful to be able to walk the non-data files in the repo, so I'm moving that part of the walk to a separate function. In particular, this allows an extension to interact with only the non-filelog store data (for instance, when cloning everything but filelogs).

clone: move file stream walk to a separate function Moves the file walk out of the stream method so that extensions can override it. This allows an extension to decide what files should be streamed, and in particular allows a stream without filelogs.

dirstate._walkexplicit: inline dirsnotfound.append

dirstate._walkexplicit: rename work to dirsfound Now that this code is factored out, work is too specific a name.

dirstate.walk: refactor explicit walk into separate function This enables this code to be reused by extensions that implement the other, more time-consuming bits of walk in different ways.

dirstate.walk: pull skipstep3 out of the explicit walk code This is a move towards factoring out this code into a separate function.

dirstate.walk: move dirignore filter out of explicit walk code This is a move towards factoring this code out into a separate function.

dirstate.walk: maintain a list of dirs not found Upcoming patches will factor out the walk over explicit files done in step 1. This helps us get there.

highlight: fix page layout with empty first and last lines Repeated newlines were stripped by pygmentize, now give the option not to do so.