Add utilities for concurrency control using pthread.

 - Type definition lsql::Lock.
 - lsql::lock for acquiring a lock.
 - lsql::unlock for releasing a lock.
Add tests and helpers for concurrency.

NOTE: These tests currently fail due to an unknown reason. This
has to be resolved as soon as possible!
Rename the BufferFrameTest file.
Add a ConcurrentMap implementation and tests.
Change the way tests are compiled.

In favor of easier compilation, all *.cpp files are included in
the main test file now. This is necessary, as otherwise independent
includes to the same source files could lead to duplicate definitions
in the linking phase.
Update the XCode project.
Fix newline file endings.
Fix the lock tests.

 - Testing the shared lock requires a different order.
 - Tests for the unlocked state needs a different thread.
Fix BufferFrame constructor const arguments.