crypt32: Use an empty string as a separator when no separator is desired to avoid special cases for NULL.

This mirrors Dan Kegel's fix for iphlpapi.

dxdiagn: Successfully copy to destination variants with an invalid type in IDxDiagContainer::GetProp.

GetProp now simply unconditionally clears the destination variant if
VariantClear fails.

widl: Check whether an expression is a constant one before assuming it is a toplevel conformance when writing conformance or variance descriptors.

This allows the code to not have to track the operator type twice.

It's only set, never read from.

It was just a simple indirection to get to a var_t, so just replace
all uses of it with the latter.

Unsized [out] strings are not allowed because of the potential to
overflow the buffer passed in.

In this case type_array_get_conformance will return NULL. The code
here is actually replacing an existing array with an EXPR_VOID
conformance with the specified conformance, so issue an error if
type_array_get_conformance returns NULL or the conformance has already
been defined.

widl: Convert assign_stub_out_args to using typegen_detect_type and fix the non-conformant array case.

msi: Implement a second cabinet extractor on top of IStream and use it to extract embedded cabinets.

Currently a cabinet stream is read into memory and then written to a file,
which is then extracted like an external cabinet file. This uses more time
and disk space than necessary and fails if the cabinet is too large to fit
into memory.

msi: Display the file identifier instead of the filename in the SelfRegModules and SelfUnregModules actions.