Public key passphrases when using ext connection method

When using the ext connection method, and a public key is found by the cvsjava implementation, it checks a System property named "maven.scm.cvs.java.ssh.passphrase". If this property is not defined, then the empty string is used as the passphrase.

The exception given when attempting to use the public key with an empty passphrase (when in reality the passphrase is not empty) is misleading and does not really tell the user that the cvsjava library could not determine what passphrase to use. In addition, the site documentation does not make any mention of the need to set the property "maven.scm.cvs.java.ssh.passphrase".

In my opinion, a mention in the site provider documentation about this property (along with several others used by ExtConnection, such as the location of the public key file, which are all undocumented) would go a long way towards helping make this plugin/provider easier to use. In addition, the exception printed in this scenario could be clearer as well.