darshan-logutils now returns an error when encountering a log file
with a module version number greater than what the library was
built with. all utilities were also updated to account for this
modification

bug reported by William Yoo

The stdio module stores names for the default streams (stdin,
stderr, stdout) in the following format: <STDERR>. The '<' and
'>' symbols require proper escape characters in order to be
properly interpretated by the darshan-job-summary (perl) script.

POSIX_F_OPEN_TIMESTAMP is now POSIX_F_OPEN_START_TIMESTAMP
POSIX_F_CLOSE_TIMESTAMP is now POSIX_F_CLOSE_END_TIMESTAMP

I also added POSIX_F_OPEN_END_TIMESTAMP and
POSIX_F_CLOSE_START_TIMESTAMP, so we can better understand how
long open and close phases are for some applications.

We don't currently have a system to try this out on, but just
wanted to make sure something was there as a failsafe. The current
implementation should be able to correctly aggregate all counters
in BGQ records, except for BGQ_INODES.

this includes defining an example logutils function for
aggregating null records into a single shared null record (needed
for darshan-merge utility)

also, bug fix to avoid any attempt of reading log file for
modules with no data present in the log