Cache: keep c->body_start when Vary changes (ticket #2029). If the variant hash doesn't match one we used as a secondary cache key, we switch back to the original key. In this case, c->body_start was kept updated from an existing cache node overwriting the new response value. After file cache update, it led to discrepancy between a cache node and cache file seen as critical errors "file cache .. has too long header".

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


ngx_include="unistd.h";      . auto/include
ngx_include="inttypes.h";    . auto/include
ngx_include="limits.h";      . auto/include
ngx_include="sys/filio.h";   . auto/include
ngx_include="sys/param.h";   . auto/include
ngx_include="sys/mount.h";   . auto/include
ngx_include="sys/statvfs.h"; . auto/include
ngx_include="crypt.h";       . auto/include