Use UDisksObjectInfo API from udisks 2.0.90, if available, for symbolic icons

Without this fix volumes would fall back to folder-remote-symbolic
which is obviosly wrong. With this fix, it looks correct, see

 http://people.freedesktop.org/~david/gvfs-udisks2-symbolic-icons.png



Right now we only use the API if it's available - things still work
with udisks >= 1.97.

Signed-off-by: David Zeuthen <zeuthen@gmail.com>