Casting the result of some #process() calls to an integer to avoid exception in Ruby 1.9.3 and up.

Casting the result of some #process() calls to an integer because,
under ruby 1.9.3 and up, nilClass does respond to '>' or '<'
operators and the comparisons on lines 102 and 120 would raise a
NoMethodError if any of the values where nil.

Ideally this would be fixed in the NewRelic::Processor::EpochCounters
class in the newrelic_plugin gem, but I don't know if 'nil' is
significant elsewhere where that gem is used.