xlock: Use (PID, TID, PC) as lock owner

Use the tuple (PID, TID, PC) as lock owner of the xseg locks.
Remove the provided owner argument and use the above triplet value as the lock
owner.
xq: Remove 'who' argument

Remove obsolete 'who' arguement, which was used as an owner for the
corresponding xlock structure. Since xlocks now creates its own owner, theres is
no need for providing an 'owner' arguement on xq API.
xpool: Remove 'who' argument
xseg: Remove redefinition of X_TRUNCATE
xseg: Bump library version to 0.4
Remove debug print message
xseg: Fix compilation warnings
xseg: Replace flag-based segment lock with an xlock
xseg-tool: Adjust lock recovery process to the new xlock owner scheme
xseg: Refactor xseg_backtrace output
xseg: Add revision to XSEG_VERSION
xseg: Remove obsolete debug message
Merge pull request #18 from philipgian/release-0.4-locks

Improve xlock
Bump version to 0.4rc2 in release branch