it seems that the kernel was not compiled to support davfs filesystem ( at least my kernel):
cat /proc/version
Linux version 2.6.38.8-pclos1.bfs (
root@localhost.localdomain) (gcc version 4.5.2 (GCC) ) #1 SMP PREEMPT Sat Jun 4 04:13:21 CDT 2011
cat /proc/filesystems
nodev sysfs
nodev rootfs
nodev bdev
nodev proc
nodev tmpfs
nodev devtmpfs
nodev debugfs
nodev securityfs
nodev sockfs
nodev pipefs
nodev anon_inodefs
nodev devpts
ext2
cramfs
nodev ramfs
nodev hugetlbfs
nodev mqueue
ext3
nodev usbfs
nodev fuse
fuseblk
nodev fusectl
nodev binfmt_misc
nodev rpc_pipefs
nodev nfsd
[EDIT]
you can try to use mount.davfs2 and umount.davfs2 provided by davfs2