Selfupdate fails after upgrading MacPorts to El Capitan version

[aaargh@…]

Output from port -d selfupdate:

DEBUG: Copying /Users/<usernamedeleted>/Library/Preferences/com.apple.dt.Xcode.plist to /opt/local/var/macports/home/Library/Preferences
DEBUG: MacPorts sources location: /opt/local/var/macports/sources/rsync.macports.org/release/tarballs
--->  Updating MacPorts base sources using rsync
receiving file list ... done

sent 36 bytes  received 69 bytes  42.00 bytes/sec
total size is 27013120  speedup is 257267.81
receiving file list ... done

sent 36 bytes  received 76 bytes  74.67 bytes/sec
total size is 512  speedup is 4.57
DEBUG: failed verification with key /opt/local/share/macports/macports-pubkey.pem
DEBUG: openssl output: Verification Failure
child process exited abnormally
DEBUG: Failed to verify signature for MacPorts source!
    while executing
"macports::selfupdate [array get global_options] base_updated"
Error: Failed to verify signature for MacPorts source!
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: /opt/local/bin/port: port selfupdate failed: Failed to verify signature for MacPorts source!

[mf2k (Frank Schima)]

Duplicate of #49233.