libfabric-2.0: fi_info changes

[shefty]

• Require that all fi_info structures come from API calls: fi_getinfo / fi_allocinfo / fi_dupinfo. No hand-crafting of the structure.
• Allows provider to allocate space beyond each structure for internal purposes.
• Add fi_fabric2() API that takes fi_info as input instead of fi_fabric_attr
• With above requirements, a hidden pointer beyond fi_fabric_attr can link back to fi_info, allowing the current fi_fabric() call to work
• New call just makes everything more intuituive