Fix unmount race condition that can trigger a kernel panic

We should not be using the mount_state field of structure fuse_data without
holding the device lock. Doing so can trigger a kernel panic:

If the FUSE device handle is closed while the corresponding volume is being
unmounted fuse_device_close might release the shared fuse_data structure before
biglock is unlocked in fuse_vfsop_unmount. Then, when attempting to unlock the
already freed biglock in fuse_vfsop_unmount a kernel panic is triggered.

Tracked as issue #77: https://github.com/osxfuse/osxfuse/issues/77
Bump version to 2.5.5
Merge branch 'osxfuse-2'

Conflicts:
	common/fuse_version.h
	fuse_device.c
	fuse_internal.c
	fuse_ipc.c
	fuse_vfsops.c
Do not hold biglock while calling a cluster I/O function

When using mount-time option nosyncwrites cluster_push will call cluster_io and
eventually fuse_vnop_strategy. This can lead to a deadlock and a subsequent
kernel panic because biglock is already locked. See 471e6bb.

The issue is addressed by releasing biglock before calling a cluster I/O
function and reaquiring it afterwards.
Add support for fcntl F_FULLFSYNC
Fix ticket reference counting

* Fix kernel panic in case fuse_vget_i fails in fuse_vnop_create

* Fix ticket leak in fuse_vnop_lookup

* Fix ticket leak in fuse_vnop_setxattr caused by not releasing the ticket in
  case fdisp_make_vp_canfail fails

Tracked as issue #84: https://github.com/osxfuse/osxfuse/issues/84
Bump version to 2.5.6
Merge branch 'osxfuse-2'

Conflicts:
	common/fuse_version.h
	fuse_internal.c
	fuse_vfsops.c
	fuse_vnops.c
Fix commit 929236f

Releasing a non-existent ticket is not a good idea.
Fix race-condition in fuse_device_read

Hold tk_aw_mtx while transferring data to user space. Otherwise the ticket's
data buffer tk_ms_bufdata might disappear on us, resulting in a "Data access"
kernel panic when calling uiomove.
Merge branch 'osxfuse-2'
Update copyrights
Add support for OS X 10.9
Add support for Clang
Bump version to 2.6.0
Merge branch 'osxfuse-2'

Conflicts:
	common/fuse_version.h
	fuse_ipc.c
	osxfusefs.xcconfig
Remove unused variable isdir
Remove unused variable data
Remove unused variables parent_nodeid, size
Remove unused variable mntflags