Make java 1.7 mandatory and refuse to run on earlier versions.

git-svn-id: http://svn.mkgmap.org.uk/splitter/trunk@309 838fabe5-b1a8-4b81-9896-7a84386980e9
Set source and target java version to 1.7 

git-svn-id: http://svn.mkgmap.org.uk/splitter/trunk@310 838fabe5-b1a8-4b81-9896-7a84386980e9