[MOD] Core, Locking: Command optimizations, seperate read/write locking
[MIN] Core, Locking: Replace empty string with constant
[FIX] Core, Locking: Fix Locking Exceptions in RESTXQ

RESTXQ shares a Context, thus storing registered flag in there
was unsafe. Moved to Progress.
[FIX] Core, Locking: Add XQuery module tests and fixups
[Core, Locking]: Remove locks not needed any more to prevent a memory leak
Merge pull request #682 from JensErat/locking

[Core, Locking]: Different fixes and enhancements