templatefilters: make json filter be byte-transparent (BC) (issue4926)
This is necessary to preserve filename encoding over JSON. Instead, this
patch inserts "|utf8" where non-ascii local-encoding texts can be passed
to "|json".
See also the commit that introduced "utf8" filter.
hgweb: add option to convert encoding of graphdata()
Because future patches will change "|json" filter to handle input bytes
transparently, i.e. use UTF-8b encoding, "{jsdata}" must keep data in UTF-8
bytes, whereas "{nodes}" are text.
This patch inserts encodestr() where localstr is likely to survive.