Fixes #3681: MPI_T performance variable implementation rollup

---svn-pre-commit-ignore-below---

r28800 [[BR]]
MCA: Per-RFC, add support for performance variables

This commit adds an API for registering and querying performance
variables (mca_base_pvar) in the MCA base. The existing MCA variable
system API has been updated to reflect the new API: MCA variable
groups have performance variables, and new types have been added (double,
unsigned long long) to reflect what is required by the MPI_T
interface. Additionally, the MCA variable group code has been split
into its own set of files: mca_base_var_group.[ch].

Details of the new API can be found in doxygen comments in the header:
mca_base_pvar.h.

Other changes to the variable system:

 * Use an opal_hash_table to speed up variable/group lookup.
 * Clean up code associated with MCA variable types.
 * Registered performance variables are printed by ompi_info -a. In the
   future an option should be added to control this behavior.

Changes to OMPI:

 * Added full support for the MPI_T performance variable interface.

r28801 [[BR]]
Add example performance variables to ob1: unexpected message queue length, posted receive length

r28802 [[BR]]
ignore unavailable components when registering

r28803 [[BR]]
Add profiling function definitions for MPI_T and add a missing type into mpi.h

r28804 [[BR]]
mpit: fix behavior when returning strings

r28805 [[BR]]


r28816 [[BR]]
Cleanup the MPIT errors - include the generated mpit lib in libompi, set ignores, remove the now unused mpit directory

r28817 [[BR]]
Fix warnings in ob1 introduced by the pvar commit

r28818 [[BR]]
Remote duplicate mpi/tool from DIST_SUBDIRS

r28913 [[BR]]
After talking with Nathan, update some comments/documentation about
the new MCA var and pvar systems.

r28943 [[BR]]
MPI_T: add man pages for MPI_T_* functions and fix typos in tool file names

r28949 [[BR]]
MCA/base: variable system updates

 * Use an enumerator to handle bool values.
 * Fix a leak in the variable enumerator.
 * Fix a leak in an orte parameter.