- read and write start timestamps should record start timestamp of first
  read/write to *begin*, not start timestamp of first read/write to
  complete
- mirrors earlier fix to open timestamps

- be careful to record start timestamp of first open to start rather
  than start timestamp of first open to complete

mount information is now sorted in order of descending mount
point lengths to fix a bug in matching file names to mount
points. the longest mount point string which matches the file
name is the corresponding mount. this change requires slight
changes to the darshan-logutils API, but does not modify the
log file format

- move fopen/fopen64 wrappers to stdio module
- make infrastructure for tracking stream pointers based on similar fd
  infrastructure in posix
- define placeholder record structs
- wrappers don't actually do anything yet

Otherwise, compile errors are generated when building an external
tool that uses the darshan-logutils api/library.

Darshan now provides debugging tips for cases where log files
are not generated.

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