Another bad file on Lion build bot

[David Evans]

The following left over file on the Lion build bot has been blocking 
builds for several perl ports today:

Error: Failed to install p5.20-yaml
DEBUG: Image error: /opt/local/lib/perl5/vendor_perl/5.20/YAML.pm 
already exists and does not belong to a registered port.  Unable to 
activate port p5.20-yaml. Use 'port -f activate p5.20-yaml' to force the 
activation.

Note this in only p5.20-yaml, not any of the other perl versions.

Builds where this occurred today are

https://build.macports.org/builders/buildports-lion-x86_64/builds/26626
https://build.macports.org/builders/buildports-lion-x86_64/builds/26630

Any help in removing this file would be greatly appreciated.

Thanks

Dave