localrepo: add a currenttransaction method This method returnx the current transaction or None: it will allow a cache writer to hook in an existing transaction.

repoview: extract actual hidden cache writing in its own function This will allow the generation of this cache within the transaction. Relying on the transaction will reduce the chance of reader seeing bad cache.

templates: fix broken "less" & "more" links in paper style (issue4460) "/search", which is an invalid command in hgweb, was mistakenly used for "[show] more [revsets]" and "[show] less [revsets]" links on search page in templates "paper" (and those which inherit paper, such as coal) before and worked fine until 6e1fbcb18a75, which made hgweb more strict about invalid commands.