javadoc fixes

git-svn-id: http://josm.openstreetmap.de/svn/trunk@5818 0c6e7542-c601-0410-84e7-c038aed88b3b
add system name to user agent string, remove direct setting of user agent in two functions, as this strips the Java part of string and is unnecessary

git-svn-id: http://josm.openstreetmap.de/svn/trunk@5819 0c6e7542-c601-0410-84e7-c038aed88b3b