nick reservation and some other settings can't be enabled via rehash

[slingamn]

We got a report in #oragono that you can't enable nick reservation via rehash. We have code support for this but it may be buggy.

[slingamn]

I found two more of these:

1. Couldn't enable vhosts via rehash
2. Couldn't enable history via rehash if autoresize-window was set