Simplify tests

git-svn-id: svn://svn.code.sf.net/p/fuego/code/trunk@1876 2e953b5c-c64d-0410-be54-f773e93e544c
Move GainsLiberties to GoBoardUtil; extract AchievesLibertyTarget from it to implement KeepsOrGainsLiberties as well

git-svn-id: svn://svn.code.sf.net/p/fuego/code/trunk@1877 2e953b5c-c64d-0410-be54-f773e93e544c
Remove assertion - IsLadderEscapeMove also works for 2-liberty blocks

git-svn-id: svn://svn.code.sf.net/p/fuego/code/trunk@1878 2e953b5c-c64d-0410-be54-f773e93e544c