crypt32: implement CryptSIPLoad (resend)

[Juan Lang]

> Most likely what you want is do a LoadLibrary in all cases and don't
> bother to cache anything, the loader will take care of the refcount.

The reason I cache is that the number of LoadLibrary calls is
potentially unknown.  Each function can have its own DLL registered in
the registry.  In my previous implementation you rejected, I enforce
that a SIP exists entirely within one DLL, as that's what
CryptSIPAddProvider allows.  By doing so, I know how many LoadLibrary
calls I've done - one for each SIP.

If I 1. allow a separate dll per function, as the registry allows, and
2. don't cache the dll names myself, I guess I must store the HMODULE
for each function?  The cache allows me to avoid that.

In this implementation, I cache each DLL, so that I only do one
LoadLibrary per dll name.  This has less memory impact than the straw
man approach I think you suggest, and is (I guess) more readable than
the one-dll-per-SIP approach.

Am I still missing something?  Thanks,
--Juan