revset: parse variable-length arguments of followlines() by getargsdict()

parser: extend buildargsdict() to support variable-length positional args This can simplify the argument parsing of followlines(). Tests are added by the next patch.

parser: make buildargsdict() precompute position where keyword args start This prepares for adding *varargs support. See the next patch.

chg: change server's process title This patch uses the newly introduced "setprocname" interface to update the process title server-side, to make it easier to tell what a worker is actually doing. The new title is "chg[worker/$PID]", where PID is the process ID of the connected client. It can be directly observed using "ps -AF" under Linux, or "ps -A" under FreeBSD.

chgserver: add the setprocname interface This allows clients to change its process title freely.

hgweb: use archivespecs for links on repo index page too Moving archivespecs to the module level allows using it from other modules (such as hgwebdir_mod), and keeping a reference to it in requestcontext allows current code to just work.

hgweb: use util.sortdict for archivespecs Thus we allow dict-like indexing and "in" checks, and also preserve the order of archive types and can generate links in a certain order (so requestcontext.archives is no longer needed).