exclude packages from javadoc generation

Hi,

I don't want to generate javadocs for all packages of my sources. I'll upload a patch that allows the user to specify a list of package names that are excluded from javadoc generation.

For instance, to exclude javadocs for package com.foo and com.foo1, the user can specify this property in the project.properties file:

maven.javadoc.excludepackagenames = com.foo,com.foo1

The generated javadocs won't contain these packages...

Maarten