Test if binary folder exists

git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25880 dab4d1a6-ed17-0410-a064-d1ae371a2980
Description:
    Minor code/comment cleanups, found while reviewing 'avoid truncate' code.

Tested on:
    MacOSX/64 10.10.1 (amazon) w/serial & parallel
    (Too minor to require h5committest)


git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25881 dab4d1a6-ed17-0410-a064-d1ae371a2980