Fixed fastcgi/scgi/uwsgi_param inheritance. The following problems were fixed: 1. Directive fastcgi_cache affected headers sent to backends in unrelated servers / locations (see ticket #45). 2. If-Unmodified-Since, If-Match and If-Range headers were sent to backends if fastcgi_cache was used. 3. Cache-related headers were sent to backends if there were no fastcgi_param directives and fastcgi_cache was used at server level.