merge in multi-y patch from https://code.google.com/p/rrd4j/issues/detail?id=8

Conflicts:

	src/main/java/org/rrd4j/core/RrdDef.java
	src/main/java/org/rrd4j/demo/Demo.java
	src/main/java/org/rrd4j/graph/RrdGraph.java
	src/main/java/org/rrd4j/graph/RrdGraphConstants.java
	src/main/java/org/rrd4j/graph/RrdGraphDef.java
	src/main/java/org/rrd4j/graph/ValueAxis.java
	src/main/java/org/rrd4j/graph/ValueAxisLogarithmic.java
	src/main/java/org/rrd4j/graph/ValueAxisMrtg.java
add in files missed in previous commit
fix compile errors
fix demo
Merge pull request #1 from brharrington/multi-y

Multi y