Handle OOM errors better

Handling this is tricky, but when we're doing memory intensive operations, we may want to try to try to deallocate big structures, warn user, and given them a chance to save their work.

java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:2219)
at java.util.ArrayList.grow(ArrayList.java:213)
at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:187)
at java.util.ArrayList.add(ArrayList.java:411)
at com.google.refine.browsing.util.NumericBinIndex.processValue(NumericBinIndex.java:265)
at com.google.refine.browsing.util.NumericBinIndex.processRow(NumericBinIndex.java:225)
at com.google.refine.browsing.util.NumericBinRecordIndex.iterate(NumericBinRecordIndex.java:64)
at com.google.refine.browsing.util.NumericBinIndex.(NumericBinIndex.java:83)
at com.google.refine.browsing.util.NumericBinRecordIndex.(NumericBinRecordIndex.java:46)
at com.google.refine.browsing.facets.RangeFacet.computeChoices(RangeFacet.java:254)
at com.google.refine.browsing.Engine.computeFacets(Engine.java:229)
at com.google.refine.commands.browsing.ComputeFacetsCommand.doPost(ComputeFacetsCommand.java:55)
at com.google.refine.RefineServlet.service(RefineServlet.java:179)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at org.mortbay.servlet.UserAgentFilter.doFilter(UserAgentFilter.java:81)
at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter.java:132)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.jetty.bio.SocketConnector$Connection.run(SocketConnector.java:228)

Start with NumericBinIndex.processValue and NumericBinRecordIndex.iterate in the stack trace, then trace how RangeFacet.computeChoices reaches Engine.computeFacets and ComputeFacetsCommand.doPost. The issue is done when memory-intensive operations handle the reported Java heap-space failure by attempting cleanup, warning the user, and providing a way to save work, but the exact behavior still needs definition.