garbage collect two unused enum mandocerr items
and fix a couple of comments while here
The previous commit to this file broke the control flow keywords \{ and \}
when they immediately follow a request or macro name, without intervening
whitespace.  Minimal fix.

The lesson learnt here is that, despite their appearance, \{ and \} are
not escape sequences, so never skip them when parsing for names.
Add a test to catch .el\{ breakage; roff.c rev. 1.88
start on being able to safely run io through the midlayer without
the kernel biglock. the plan is to have the midlayer assume its
running without the biglock, but that it cant call adapters or
devices without taking the biglock first.

this diff just wraps the calls to the adapter iopool get and put
handlers up in the biglock.

this is safe now because of kettenis' commit to src/sys/kern/init_main.c
r1.120. ive been running this in various places since early 2011.
take the biglock when calling an adapters scsi_cmd handler.