GitLab

User on OpenMPI list wanted to create a 259 character file.  shared file
pointer name construction used the magic '256' value to construct a full
path to the hidden shared file pointer file.  PATH_MAX already exists
for this purpose, so use it.

While there, found a few spots checking/setting PATH_MAX, so do that in
one place

Closes #2212
Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>