Allow `mvn` to be redefined so we can use `mvn3` explicitly in the
MacPorts port.

Need to remove the "-SNAPSHOT" string from the tagged version.

Make it so that we can actually add a proper message to the tag
generated by Maven.

That command resulted in this error:

    [INFO] [ERROR] Failed to execute goal
    org.apache.maven.plugins:maven-deploy-plugin:2.8.2:deploy
    (default-deploy) on project pdf-form-replace-font2: Deployment
    failed: repository element was not specified in the POM inside
    distributionManagement element or in
    -DaltDeploymentRepository=id::layout::url parameter -> [Help 1]

I had added `release:perform` because it's described as the second step
in releasing in this document:
https://maven.apache.org/maven-release/maven-release-plugin/usage.html

However, as explained in
https://maven.apache.org/maven-release/maven-release-plugin/usage/perform-release.html
, `release:perform` runs the `deploy` target, which doesn't make sense
for this project. It seems like we only need `release:prepare` to do a
Maven-driven release.

When I tried packaging with MacPorts, the path written to the shell
wrapper was the temporary MacPorts build path, not the final install
path.

My plan is to extract the shell wrapper build to the `package` stage,
and do something with the variables to give it the correct install path.
Not sure what that something is yet, but that's the idea.