[PATCH 00 of 23 Series-D] hgweb cleanup and filtering (do not be scared by the length)

[Pierre-Yves David]

This series prepare hgweb for filtering and enables it

I found several piece of code needing attention so the series is a bit long, but
all changes are pretty trivial:

You can review it with the slicing bellow

hgweb: no do not use listinsert(0, ...)
hgweb: renamed `limit` argument to `lastest`

hgweb: do not compute graph is there is no revision to graph
hgweb: walk the graph through the changelog

hgweb: use changelog for iteration

(here his my new best enemy: revnavgen function)

hgweb: document the revnavgen function
hgweb: move revnavgen into an object
hgweb: pass nodefunc to the revnav object
hgweb: move the `seq` closure into a dedicated function
hgweb: drop recursivity in _navseq
hgweb: better names for _navseq argument
hgweb: ensure _navseq yield strictly increasing numbers
hgweb: move hex creation into an object method
hgweb: do not access first changeset with a string
hgweb: simplify return value creation in for navgen
hgweb: simplify the handling of empty repo
hgweb: simplify addition of "(0) navigation entry"
hgweb: introduction a filrevnav subclass
hgweb: pass repo object to revnav construction
hgweb: generate revnav in two phase
hgweb: ignore filtered revision in revnav
hgweb: protect filelog revnav from filtering related crash

hgweb: run with "unserved" filter