make jsextensions docs known to Qt Creator

Change-Id: I1c00a577b8b94c5114138b35da1f7e15ddad3344
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Doc: extensions to JavaScript built-ins

Change-Id: Ia19ed4f48e19c28a2a78d294d4671e3efaf32c9c
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
introduce Array.uniqueConcat

Preparation for fixing QBS-501.

Change-Id: I00fee37347e320de4a598da093a8eb99df934d55
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>