[PATCH] hgweb: load extensions explicitly (issue1824)

[Yuya Nishihara]

This is another solution for issue1824.

This only affects hgweb, not third-party tools, and even
NOT hgwebdir unfortunately.

It seems ugly to duplicate code snippet found at _dispatch().

> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1256742908 -32400
> # Node ID bda617e9df583a8adb4380acc98f8d2ca4e548d5
> # Parent  ccf1bfe1806de0789b815b1ad4ac22dbaac95ae3
> hgweb: load extensions explicitly (issue1824)