xseg: Support X_TRUNCATE operation
xseg: Fix bug in return value
xseg_posixfd: Fix buffer overflow in posixfd_init_signal_desc

The length passed in hexlify() must be equal to the half
of the POSIXFD_FILENAME_LEN because hexlify() computes hashes
in pairs based on the address of the signal descriptor pointer.

Also double the size of the name of the signal descriptor.
xlock: Add UNKNOWN_OWNER
xlock: Rename Noone to XLOCK_NOONE
xlock: Add XLOCK_XSEGTOOL owner
xseg: Use the newly introduced XLOCK_UNKNOWN_OWNER

Change all xlock_acquire occurrences where a dummy owner value was used, to the
new XLOCK_UNKNOWN_OWNER value.
xseg-tool: Use the reserved XLOCK_XSEGTOOL owner
xseg-tool: Remove unused port args from failport
xseg-tool: Add recover locks command