BSTR caching

[Markus Stockhausen]

> I'm not sure about the exact details of what this should fix, but
> wouldn't using a private heap have mostly the same effect?

Hi Henri,

it will definitely fix bug 12460 (self tested) and maybe 3756 as it
implements deferred release of BSTR memory. It does not matter if we are
using private heap or global heap. Important is, that the allocated
memory constantly survives a SysFreeString call until the next
SysAllocString call ist started. 

Related information:
http://www.winehq.org/pipermail/wine-devel/2009-October/078957.html
http://bugs.winehq.org/show_bug.cgi?id=3756

Additionally it reduces the time for Dealloc/Alloc Cycles of BSTR memory
in best cases by about 50%. 

Best regards.

Markus