TAKE - Implement vnode tracing.

[Ted Kline <jtk@xxxxxxx>]

Implement an optional (via config) vnode tracing functionality..

Run your favorite form of make config/oldconfig/xconfig and select
"CONFIG_XFS_VNODE_TRACING" under XFS in the filesystem section.

i.e.:

>> 
>> [1]kdb> vnode 0xc2b58008
>> vnode: 0xc2b58008 v_count 2 type VDIR
>>    v_inode 0xc27b7700 v_bh->bh_first 0xc275c268 pobj 0xc275c250
>>    ops xfs_vnodeops
>>    v_trace 0xc3fa0920