Default build properties based on PYTHON_PATH and JAVA_HOME

[JosephCottam]

Give a chance for zero-configuration development by providing a "default.properties" file that derives java.path, python.path and python.version information from environment variables. The build file loads the system.properties first, then default.properties, so the defaults can be ignored BUT there is at least a chance things will build without needing to do configuration first.

Note: default.properties will be in version control, but system.properties will not be.

See http://www.ibmpressbooks.com/articles/article.asp?p=519946&seqNum=2 for why this solution works and is reasonable.

[JosephCottam]

The location of java headers differs relative to the JAVA_HOME based on the OS & java implementation (Oracle vs. OpenJDK)...makes this technique more hit-or-miss than hoped.