hgweb: call process_dates() via DOM event listener
All the hgweb templates include mercurial.js in their header. All
the hgweb templates have the same <script> boilerplate to run
process_dates(). This patch factors that function call into
mercurial.js as part of a DOMContentLoaded event listener.
[hgk]
path = /usr/share/mercurial/hgk