this allows us to request memory allocations at smaller granularity
than MiB

Signed-off-by: Cong Xu <cong.xu@intel.com>

Signed-off-by: Cong Xu <cong.xu@intel.com>

This is needed to distinguish between log files generated with
the same job id (i.e., for jobs that have multiple steps)

This function can be called by modules to allow FS-specific
modules to gather data for a given file path/file descriptor.
Currently integrated into POSIX and STDIO modules.

some bugs were causing the regression tests to fail when using
LD_PRELOAD instrumentation method

rather than using 'begin_shutdown', 'get_output_data', and
'shutdown', we combine all three into one shutdown routine.

Cleanup the structure and documenation of the code to be in sync
with the new mmap version of Darshan. In particular, I made sure
all extra mmap logic was properly ifdef wrapped so it's more clear
which portions of the code are responsible for implementing that
feature.

This interface provides some convenience functions for mapping
opaque record identifiers (could be a filename, file descriptor,
or any other type of file handle) to a corresponding runtime
structure referencing the actual file record. This runtime
structure should at least contain a pointer to the actual file
record, and can also persist arbitrary state for this record.

- memory management is now entirely handled by darshan-core for
  module records
    * when registering new records, darshan-core returns the
      corresponding buffer to write it to, rather than allowing
      module to determine this
- modules now decide whether darshan-core should track record
  names by passing either a valid name or NULL to the register
  function
    * this allows modules to register records that aren't really
      tracked by darshan-core
- only the POSIX module has been ported to new changes for this
  commit

also some code clean up to change references of record hash
to name hash to be more clear about what it is actually storing.

checkpoint of code that populates OST and MDT counts per file system--doesn't seem to work though...

the POSIX module will call into the Lustre module for each file
record created that corresponds to a file from a Lustre FS. No
counters are currently stored but most of the module strucutre
has been stubbed.

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