doesn't keep track of anything yet.

Renames some sview variables for better clarity and put some node
  fields into alphabetic order

This commit adds support for free_mem as part of the sinfo
command using the key 'e' ('f' and 'F' are already taken).

This commit adds information about the free memory to the
output created by slurm_sprint_node_table(). The unit of
FreeMem is MiB like RealMemory.