fix declaration-after-statement warnings of ruby trunk
fix declaration-after-statement warnings of ruby trunk

The commit https://github.com/ruby/ruby/commit/bd0a9d2fb603d308086b37499773bae50065a1fa
adds -Werror=declaration-after-statement. This may cause an error and make gem installation fail
See http://www.ruby-forum.com/topic/714046

mongodb/mongo-ruby-driver,fairplace/mongo-ruby-driver,ShanaLMoore/mongo-ruby-driver,estolfo/mongo-ruby-driver,0x00evil/mongo-ruby-driver,namusyaka/mongo-ruby-driver,jonhyman/mongo-ruby-driver,aherlihy/mongo-ruby-driver,brandonblack/mongo-ruby-driver,mongodb/mongo-ruby-driver,fhwang/mongo-ruby-driver,agis-/mongo-ruby-driver,AndyObtiva/mongo-ruby-driver,wandenberg/mongo-ruby-driver,malditogeek/mongo-ruby-driver,dunedain289/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,estolfo/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,tommyb67/mongo-ruby-driver,xronos-i-am/mongo-ruby-driver,kay-kim/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,saghm/mongo-ruby-driver,saghm/mongo-ruby-driver,mongodb/mongo-ruby-driver,kay-kim/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,malditogeek/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,jonhyman/mongo-ruby-driver,malditogeek/mongo-ruby-driver