added the option to the GC.HeapDump jcmd, to create gzipped heap dumps.
added the feature to heap dumps via jmap. But the heap dumps created via -XX:+HeapDumpOnOutOfMemoryError are currently always uncompressed.
This should be changed by adding a command line flag which lets the user specify the compression level of the created heap dump. The default would be to not compress the dump (as it is today).