A filename to label translation daemon

We know that utilities like install disable their SELinux support
because of the enormous amount of time it takes to load the matchpathcon
regex database.  We know that systemd spends time loading the database
at least twice.  Other utilities like the krb5libs complain about the
size and time it takes to load the database.  We've added hacks (I
believe all in Fedora, but maybe upstream as well) which try to pare
down the database to some prefix(es) on database load.  If systemd only
needs to label in /var why load all the stuff for /etc?  These prefix
hacks don't work particularly well as fallback labels (such as
default_t) are hard to capture and the prefixes cannot be long as the
regexes are usually quite short.  They also don't work well with label
equivalencies.

So today I wrote a little daemon which listens in the abstract namespace
for requests and returns the context.  It really really rough, I admit,
but it works quite well.  My first perf numbers looking at /home/eparis
make sense:

$ ./initonce /home/eparis
 0.180 seconds used by the processor.
$ ./initalways /home/eparis
 19.200 seconds used by the processor.
$ ./client /home/eparis
 0.570 seconds used by the processor.

If I init the DB one time and do the same lookup (for /home/eparis) 1000
times it takes .18 seconds.  Doing 1000 lookups init-ing and fini-ing
the db every time it took 19.2.  Connecting to the server and asking
1000 times took .57 seconds.  This means that if you have to do about 48
lookups, it's faster to do your own init.  If <48, you should use the