autoconf: search for uuid_parse in system libs

AC_SEARCH_LIBS will first try to resolve uuid_parse in the system
libraries (OSX), and then will try other libraries (e.g. libuuid).
UUID_LIBS is defined, containing the necessary libraries to link
against.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>

Squashed:

configure.ac: fix typo setting UUID_LIBS

Signed-off-by: Alan Somers <asomers@gmail.com>
xattr: test for xattr routine variants

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
FIXME: sockaddr encoding

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
client: add O_[DR]SYNC definitions

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
WIP: sync_filesystem

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
filestore: fix btrfs/zfs missing defs

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
filestore: check for fiemap

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
FIXME: hack portable timegm

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>