- 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

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

user can now give a config option or use a runtime environment
variable to control darshan's per module memory requirements.

this indicates whether the log file is complete or only partially
written

* header is now raw uncompressed, rather than gzip format
* mapping info stored in header is now in uncompressed terms
* storing mapping info for job data now