ACLiC build-dir creation issue (non-fatal)

I don't think this is a high-priority bug, but I figured I would flag it in case it is an easy fix.

Found I am getting this error on the ifarm:

/farm_out/brads/polhe3-50k-test-95-24851571-farm180242.err:
Warning in <ACLiC>: Could not create the directory: /tmp/tmp.pMQRdGNrhf-hcana-brads//u/group/c-polhe3/Users/brads/SWIF/hallc_replay/./SCRIPTS/src
Warning in <ACLiC>: Output will be written to /tmp/brads

Note the second ACLiC Warning indicates fallback is /tmp/brads/. That is at least local to a node, which limits the multi-job race condition, but multiple jobs can certainly fire off on a single node. I really don't know if slurm uses any namespace tricks to isolate /tmp from other jobs...

This would be associated with the .rootlogon.C "build directory" code and, I think, some bug/limitation in ROOT with creating a multidirectory path structure maybe?

FWIW, 'mkdir -p' can handle the above just fine. One of the reasons I suspect something about an OS-independent internal 'mkdir' implementation in ROOT. For example, this works fine on the ifarm nodes:

  % ROOT_BUILD_TMPDIR='/tmp/tmp.pMQRdGNrhf-hcana-brads'
  % mkdir -p '${ROOT_BUILD_TMPDIR}//u/group/c-polhe3/Users/brads/SWIF/hallc_replay/./SCRIPTS/src'