_id must go first + test for updating accross indexes
Merge pull request #69 from twillouer/idfirst

_id must go first + test for updating accross indexes
Merge remote-tracking branch 'github/master' into index2d

Conflicts:
	src/main/java/com/foursquare/fongo/impl/Util.java
	src/test/java/com/foursquare/fongo/FongoIndexTest.java