encoding: avoid cyclic dependency around "parsers" in pure Python build 80f2b63dd83a brought "asciilower" and "import parsers" into "encoding.py". This works fine with "parsers" module in C implementation, but doesn't with one in pure Python implementation, because the latter causes cyclic dependency below and aborting execution: util => i18n => encoding => parsers => util This patch delays importing "parsers" module until it is really needed, to avoid cyclic dependency around "parsers" in pure Python build.

pull: add source information to the transaction The source information can, should be applied once when opening the transaction for the pull. This will lets element processed within a bundle2 be aware of them and open the door to running a set of hooks when closing this pull transaction. This is similar to what is done in server's unbundle call.

changegroup: store source and url in the `hookargs` dict We store the source and url of the current data into `transaction.hookargs` this let us inherit it from upper layers that may have created a much wider transaction. We have to modify bundle2 at the same time to register the source and url in the transaction. We have to do it in the same patch otherwise, the `addchangegroup` call would fill these values and the hook calling will crash because of the duplicated 'source' and 'url' arguments passed to the hook call.

prechangegroup: use hook argument from the transaction There can be useful data in there (eg: bundle2 related one)

addchangegroup: call `prechangegroup` hook after transaction retrieval We want to reused some possible information stored in the transaction `hookargs` dict that may be stored by something handling the transaction at an upper level (eg: bundle2) So we move the running of the hooks after transaction creation. This has no visible effects (but an empty transaction roolback if the hook fails) because nothing had happened in the transaction yet.

addchangegroup: get the `node` argument of `incoming` hook from transaction The transaction is now carrying hook-related informations. So we use it to retrieve the `node` argument. This will also carry around all kinds of other useful informations (like: "are we in a bundle2 processing")

dicthelpers: delete now that they are no longer used

manifest: transpose pair of pairs from diff() It makes more sense for the file nodeids and returned from diff() to be ((n1,fl1),(n2,fl2)) than ((n1,n2),(fl1,fl2)), so change it to the former.

manifest: for diff(), only iterate over files, not flags From manifest.diff(), we return a dict from filename to pairs of pairs of file nodeids and flags (values of the form ((n1,n2),(fl1,fl2))). To create this dict, we currently generate one dict for files (with (n1,n2) values) and one for flags (with (fl1,fl2) values) and then join these dicts. Missing files are represented by None and missing flags by '', but due to the dict joining, the inner pairs themselves can also be None. The only caller, merge.manifestmerge(), then unpacks these values while checking for None values. By inlining the calls to dicthelpers and simplifying it to only iterate over files (ignoring flags-only differences), we can simplify life for our caller.

manifest: repurpose flagsdiff() into (node-and-flag)diff() The manifestdict class already has a method for diff flags between two manifests (presumably because there is no full access to the private _flags field). The only caller is merge.manifestmerge(), which also wants a diff of files between the same manifests. Let's combine the code for diffing files and flags into a single method on manifestdict. This puts all the manifest diffing in one place and will allow for further simplification. It might also be useful for it to be encapsulated in manifestdict if we later decide to to shard manifests. The docstring is intentionally unclear about missing entries for now.