Require fuse >= 2.7.3

FUSE for OS X is based on Linux FUSE 2.7.3. Therefore we need to lower the
required FUSE version from 2.8.3 to 2.7.3.
G_GUINT64_FORMAT expects values of type gint64

Add cast to gint64 to address the following warnings on OS X:

file_io_ops.c: In function ‘fileio_read_on_con_cb’:
file_io_ops.c:751: warning: format ‘%lu’ expects type ‘long unsigned int’, but argument 2 has type ‘off_t’
file_io_ops.c:751: warning: format ‘%lu’ expects type ‘long unsigned int’, but argument 3 has type ‘long long unsigned int’
Port RioFS to OS X
Add build instructions for RioFS on OS X
Add RioFS Xcode project
Add OS X PKG_CONFIG_PATH note

pkg-config might not find FUSE for OS X without adding /usr/local/lib/pkgconfig
to PKG_CONFIG_PATH.
Disable optimization for debug builds
select is the preferred libevent backend method on OS X

Avoid backend methods kqueue and poll. Both are known not to be working with
FUSE for OS X.
Fix unmounting and signal handling on OS X

On OS X a FUSE volume needs to be unmounted before exiting the event loop.
Unmounting the volume flushes the kernel's unified buffer cache, which results
in file system requests, that need to be handled by the event loop.

Exiting the event loop without unmounting causes the file system daemon to hang
for daemon_timeout seconds (defaults to 60 seconds) and can result in data loss
or corruption.
Remove obsolete TODOs introduced in 87efcab
Unify unmount behaviour on Linux and OS X

Unmount volume before exiting the event loop.
Tweak test_file_io for OS X

* Specify mount-time option nolocalcaches to disable kernel-side caching
* On OS X we use plain old umount instead of fusermount to unmount volumes
Add direct_io note for OS X
missing time.
Merge branch 'osx_port' of github.com:bfleischer/riofs into bfleischer-osx_port