Add comment: strings in values[] can be free()'d after mca_base_var_enum_create() returns
Expand the "btl_usnic" MPI_T enumeration to have strings of the form:

   <usnic device name>,<eth device>,<ip address>/<CIDR prefix>

For example:

   usnic_0,eth4,10.1.0.15/16

This is just handy for mapping the usnic_X device back to the IP
network to which it corresponds.
Arrgh -- remove debugging printf.
Silence warning
Silence warning

Refs #3898