[openib-general] Start of userspace verbs support

[Roland Dreier]

I've just committed skeleton versions of userspace/libibverbs and
userspace/libmthca.  This is mostly to get early feedback on the
structure of the code, etc. -- what's there doesn't do much that's
useful.  libibverbs is the device-independent part of userspace verbs,
and is what applications actually link to.  libmthca is
device-dependent support for the same set of Mellanox HCAs as mthca
support in the kernel.

Right now, about all you can do is build the libraries, set
OPENIB_DRIVER_PATH to a path where mthca.so can be found, and run
ib_devices to get a list of devices and node GUIDs.

All comments and suggestions welcome as usual.

Thanks,
  Roland