ORTE: undeprecate -x var=val in mpirun

mpirun -x var=val is back, actually it is useful alias for -mca mca_base_env_list "var=val"
btl/vader: fix a typo in mca_btl_vader_put_knem
Fix SLURM PMI2 component. set s2_nrank to the relative position of a process inside the node
(not relative position of a node inside the allocation).
mca base: fix trivial typos in help message
Merge pull request #267 from artpol84/s2_fix

Fix SLURM PMI2 component. set s2_nrank to the relative position of a pro...

Good catch!
Merge pull request #265 from miked-mellanox/topic/undeprecate_env_x

ORTE: undeprecate -x var=val in mpirun

Looks okay to me - thanks!
btl/vader: don't assume the address in the put/get segment is unmodified when
using knem

It is valid to modify the remote segment that will be used with the
btl put/get operations as long as the resulting address range falls in
the originally prepared segment. Vader should have been calculating the
offset of the remote address in the registered region. This commit
fixes this issue.