Add the MSI-specific flag '-add-msi-se' to the 'sign' command for explicitly adding a MsiDigitalSignatureEx section.
Remove NO_MSI_DIGITALSIGNATUREEX ifndefs.
Add sanity check for the potentially 'dangerous' combination of -add-msi-dse and -nest.

We don't want osslsigncode to emit bad signatures when we can avoid it.
Remove reference to exsig in msi_verify_pkcs7 to fix the -DGSF_CAN_READ_METADATA build.

This was broken due to the refactoring that happened during
the introduction of nested signature support.
version 1.7.1