swdb: Take signing key from ~/.gnupg-autogen.rc
Right now I have this in my .gnupg-autogen.rc:
- The key used to sign the SWDB. Uusally the same key as the release
- signing key. I currently stick to my older RSA key until my newer
- signing key is distributed so that building older version still
- works. SWDB_SIGNKEY=0x249B39D24F25E3B6