Since we had to modify HDF5/PnetCDF linker flags to work on Cray
by undefining appropriate symbols, we need to update the linker
options used in darshan-config. darshan-config linker options need
to include the stubs libraries and use '--start-group' and
'--end-group' flags to resolve the symbols correctly

moved most test programs and previous darshan output
to the 2.x directory

this reorganization prevents darshan from being "enabled"
(i.e., accessible to modules) until the initialization
has completely finished.

- prevents inadverdent disabling of Darshan on some MPICH builds
- fixes #94

fixes #174