OpenSSL prints normal DSA key notices to stderr. Windows PowerShell treated
those notices as terminating errors under Stop and aborted before signing.
Keep native calls under Continue, then reject nonzero exit codes explicitly.
Use the same invocation helper for installer signing.
Verified on Windows: a native exit 0 with stderr succeeds, exit 7 is rejected,
and the error preference is restored. The full production dry run passed its
format/analyze checks, all 76 tests, the Windows build, Inno Setup packaging,
DSA key matching and installer-signature verification for 1.0.7+10.
sindoring