Option to enable vld for release builds

[PhilLab]

If it is technically possible, it would be great to have the possibility to link and use VLD in your release build (of course with an option which is set to off by default).

This would then allow e.g. adding a call parameter to one's console application enableMemoryLeakDetection which could then be set by a Continuous Integration testing server to examine if new code caused new memory leaks.

[reid-p]

try compiling with VLD_FORCE_ENABLE