Cryptovec/Windows: Add reference counting per Page, improve error-msg

[amtelekom]

Hi,

the current CryptoVec implementation on Windows unlocks memory pages too early if the backing stores of multiple CryptoVecs are located in the same page.

This is because VirtualLock/Unlock do not implement reference-counting on the OS side:

This function is not like the GlobalLock or LocalLock function in that it does not increment a lock count and translate a handle into a pointer. There is no lock count for virtual pages, so multiple calls to the VirtualUnlock function are never required to unlock a region of pages.

This PR adds userspace lock counting, so only once the last CryptoVec has released it's memory from a Page, the Page is unlocked.

[Eugeny]

Looking good now - thank you!