If a file doesn't use the file command (either \file or @file),
Doxygen won't try to process it.
These declarations also turned up a doxygen warning for
crypto_ope.c; I fixed that too.
This change also makes tor_ersatz_socketpair() follow the same
interface as socketpair() rather than tor_socketpair(), so it now
needs to be wrapped in the same code as socketpair() does.