mtl/psm: do not limit PSM to 8191 context ids

The old default context id maximum was committed to the trunk in
2006. After some discussion with Intel it appears this is restricting
the mtl to an arbirarly small number of communicators. Increasing the
default to allow up to 2^16 - 1 context ids.

Refs #4574

cmr=v1.8.2
sbgp/ptp: fix obvious typo

cmr=v1.8.2:reviewer=manjugv
Fix MPI_T issues identified by friendly users.

Several fixes:

 - I was allowing an MPI_T_cvar_handle to be created for an invalid
   variable. Fixed this by checking if the variable is valid in
   mca_base_var_get.

 - Use a better error code when the caller tries to create an unbound
   pvar handle for a bound variable.

 - Return the verbosity level in MPI_T_cvar_get_info.

cmr=v1.8.2:reviewer=jsquyres
rte_base_frame.c: add sanity check to ensure proper sizes

There's a requirement in several places (e.g., opal dstore) that
sizeof(ompi_process_name_t) -- which comes from the compile-time
selected ompi/mca/rte component -- is equal to sizeof(uint64_t).  If
it's not, Bad Things will happen.

So put an assert here to catch that case.
When we comm_spawn, we really want to respect the original -host directives and not expand the daemon virtual machine unless directed to do so in the comm_spawn command. Otherwise, we will automatically launch daemons on every node in the allocation.

cmr=v1.8.2:reviewer=rhc:subject=respect vm boundaries during comm_spawn
bcol/basesmuma: close mmapped file descriptor

Not closing this file descriptor will cause us to leak file
descriptors. It is safe to close the file after it has been mmapped.

cmr=v1.8.2:reviewer=manjugv
btl_usnic_cclient.c: update to use the new opal dstore

Use the new opal dstore API (vs. the old RTE DB API).

(dstore is not going to the v1.8 series, so there's no need to CMR
this to v1.8)