Bug 2870: --disable-auth does not work

Bug 2870: --disable-auth does not work

This patch attempts to make it work by removing libauth.la and all component
functionality which depends on it. So far this reduces the minimal squid
binary by a further 900 KB on disk.

It also means anything which requires an authentication process wont work.
They get wrapped in USE_AUTH or if its a specific type with the relevant
HAVE_AUTH_MODULE_* wrappers.

So far this does:
 * FTP and CacheMgr dependency on --disable-auth-basic is already committed
 * cache_peer login= functionality is greatly reduced under various
   combinations of --disable-auth, --disable-auth-basic and
   --disable-auth-negotiate
 * peering userhash algorithm is removed
 * delay pools class 4 is removed
 * ACLs testing username are dropped.

Additionally since external ACL user= field is used interchangeably in
several places with a full login and with the right helper can be
considered a full side-band authentication I have disabled the
ExtUser/ext_user components as well.

NP: pinning is not strictly dependent on NTLM, we may use it for other
    things without involving auth so left most of it in. Just the logics
    which use auth to set the pinning flag are now removable.

IDENT not being an authentication mechanism is also left in.