hgweb: insist http_status value is a sysstr...
hgweb: insist http_status value is a sysstr
My previous change was extremely confusing to figure out, because I
thought I was looking at a client-side problem. For the low cost of an
isinstance assert, we can make those errors not happen in the future.
Differential Revision:
https://phab.mercurial-scm.org/D3727