add new code paths for getattr operations:

 - modified index_getattr_size to take a stat struct since we want to
   allow it a shot at updating the m/a/c times like the current code does.
   also, pass in the openHosts and validMeta sets, so index can optimize
   on that info (if it so chooses ... it can ignore too).

 - Container::getattr() now takes a plfs_physpathinfo, since it is
   helpful for us to be able provide it as a param in order to call
   back into the the ContainerIndex code.   Note that this means that
   the ContainerFD getattr path (fgetattr) is going to need to provide
   a physpathinfo in order to call us.  this is in-line with the
   architecture document where it seemed like we needed to consolidate
   openfile path info into a physpathinfo in Container_OpenFile.
   (We'll add a function to make a copy of it when we open and stash
   it in...)

 - checked and added back some code for handling file metadata in the backend