memoised values in the input channels
don't serialise tags if for tagged elements if there is only one tag
using a weak hashmap to memoise wireformat metadata
use the same grouping instance if there is just one tag
added a variable in the MscrMapper to know if there are reduce tasks without using the configuration all the time
using the same tag value if there is only one tag
removed warnings in the build file
memoised the writable comparator