On/off switch for ETags cache

[dread]

• Use config variable to switch ETags caching on or off. Consider joining in with 'cache_enabled'.
• Default setting for (all) caching should be off.
• Needs documenting in configuration.rst

[dread]

dread:

] That's the proxy_cache decorator which sets a Beaker expiry time only. ] Whether that is on or off, you still end up run the ] "etag_cache(cache_key)" command in the package controller won't you? ] And won't that will either insert the Etags header or abort 304 for a ] repeat? I must admit I've not tried it, asking purely with the code in ] front of me and welcome you pointing out where I've gone wrong.

ww:

Right. So those etag calls predate the cache decorators and should probably be either moved up into the decorator (e.g. use @ckan_cache instead of @proxy_cache) or wrapped in a check for the config parameter. (And @ckan_cache could be changed to use pylons' etag_cache function rather than just setting the header...)

[dread]

Basic on/off switch added, tested & documented in cset:0da189c9630e on default.