Stop ignoring hidden service key anonymity when first starting tor

Instead, refuse to start tor if any hidden service key has been used in
a different hidden service anonymity mode.

Fixes bug 20638; bugfix on 17178 in 0.2.9.3-alpha; reported by ahf.

The original single onion service poisoning code checked poisoning state
in options_validate, and poisoned in options_act. This was problematic,
because the global array of hidden services had not been populated in
options_validate (and there were ordrering issues with hidden service
directory creation).

This patch fixes this issue in rend_service_check_dir_and_add, which:
* creates the directory, or checks permissions on an existing directory, then
* checks the poisoning state of the directory, then
* poisons the directory.

When validating, only the permissions checks and the poisoning state checks
are perfomed (the directory is not modified).