Remove duplicate terms from presearcher query

Conflicts:
	src/main/java/uk/co/flax/luwak/presearcher/MultipassTermFilteredPresearcher.java
	src/main/java/uk/co/flax/luwak/presearcher/TermFilteredPresearcher.java
Merge branch '1.1.x_merged' into prog1

Conflicts:
	src/main/java/uk/co/flax/luwak/presearcher/MultipassTermFilteredPresearcher.java
	src/main/java/uk/co/flax/luwak/presearcher/TermFilteredPresearcher.java
Handle empty terms