Add method to copy an AggregateCall, changing only its name.
Add conjars repo; now "mvn clean install" should work even if you have not previously installed linq4j.
Major improvements to null semantics. Before calling a builtin method or operator that is strict (i.e., produces null result iff one or more arguments are null, which is most of them), we check whether the arguments are null. This allows us to always pass primitive values. During code generation, we keep track of which expressions we have previously checked are not null.