Allow the nodemap to contain multiple nodes for mibs like IF-MIB

In the IF-MIB, "interfaces" and "ifMIBObjects" both contain
significant subtrees.  Allow nodemap to contain a comma-separated
list of nodes, to handle MIBs like this.
David Jarvie's patch for bug 2507
Merge branch 'V5-4-patches' into V5-5-patches

* V5-4-patches:
  David Jarvie's patch for bug 2507
Merge branch 'V5-5-patches' into V5-6-patches

* V5-5-patches:
  David Jarvie's patch for bug 2507
Merge branch 'V5-6-patches' into V5-7-patches

* V5-6-patches:
  David Jarvie's patch for bug 2507
Merge branch 'V5-7-patches'

* V5-7-patches:
  David Jarvie's patch for bug 2507
  Allow the nodemap to contain multiple nodes for mibs like IF-MIB