A console driver that wraps another with a spinlock.  We usually don't want
spinlocks, but if we want to debug the scheduler, we have to use them here.

I've also added an osv/ prefix to make sure we don't clash with system headers.

We probably should either adopt this globally or drop it, but I fear we'll run into
problems with the latter approach.

this allows the stdio code to figure out if it should go into line
buffered mode.

This will allow for easy addition of the vectored and positional I/O
syscalls, as well as making the structure of the I/O path more similar
to *BSD and Solaris.

Create a central place the managed the console driver (just isa-serial for
now), and exposes them as a device file and to the debug output routines.

This is the low-level console abstraction and should deal in the
char * hardware format.  The upper layer (debug.cc) already handles
all conversion from std::string and boost formats.