Silence boring Eclipse warnings: feature warnings - take #2

Silencing boring warnings allows seeing the interesting ones. Here I've excluded
reflectiveCalls, since that's a useful warning.
However, silencing those warnings in *Eclipse* would require committing Eclipse
projects, something which *will* take extra effort; I verified that the warnings
disappeared from the output of compilation in SBT.
Enable Java -Xlint warnings, excluding serialization-related ones