Deploy -sources JARs to Maven repository

For a number of reasons, it is very useful to have these sources JARs
deployed. For example, in Eclipse, you can right-click on a Maven JAR
dependency and choose Maven > Download Sources, and it will then
automatically download the sources JAR and link them for debugging.
Merge pull request #531 from melissalinkert/rebased/dev_4_4/maven-sources

Deploy -sources JARs to Maven repository (rebased onto dev_4_4)