Check rb_setselect usage

[ariscop]

6c2035a and similar changes need to be checked, libratbox's epoll loop is edge triggered but the code assumes it's level triggered

Since the change itself was to avoid an infinite loop, it may be best to change the event loop so this sort of code can be used to avoid callback recursion

Options:

• Always call setselect before an fd might be written to, instead of after as rb_helper is currently doing
• Level triggered + EPOLLONESHOT, might actually be the best option

There's about 80 rb_setselect calls that would need to be checked

[ariscop]

This should be done with #94 since our libratbox is going to have less and less in common with charybdis's over time