- also rename option for newer API
- make the two options mutually exclusive

This reverts commit 3f12e721.

(Previous stronger language was more accurate)

Signed-off-by: Phil Carns <carns@mcs.anl.gov>

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

use --with-max-records at configure time to change from default
of 2048 records

- contributed by Kay Thust