Prefer IPv4 connections

In some distributions (such as Debian, for example) net.ipv6.bindv6only=1 is
set by default. In some configurations, networking in java applications will be
broken. Someone recently came into #i2p experiencing this very problem.

This change closes #464.

installer/resources/runplain.sh

@@ -17,6 +17,6 @@ I2PTEMP="%SYSTEM_java_io_tmpdir"
 export CP="${I2P}" ; for j in "${I2P}/lib/*"  ; do export CP="${CP}:${j}" ; done;
 JAVA=java
 
-JAVAOPTS="-Djava.library.path=$ {I2P}:${I2P}/lib -Di2p.dir.base=${I2P} -DloggerFilenameOverride=logs/log-router-@.txt"
+JAVAOPTS="-Djava.net.preferIPv4Stack=true -Djava.library.path=$ {I2P}:${I2P}/lib -Di2p.dir.base=${I2P} -DloggerFilenameOverride=logs/log-router-@.txt"
 nohup ${JAVA} -cp "${CP}" ${JAVAOPTS} net.i2p.router.RouterLaunch > /dev/null 2>&1 &
 echo $! > "${I2PTEMP}/router.pid"

installer/resources/wrapper.config

@@ -60,6 +60,7 @@ wrapper.java.additional.2=-Dorg.mortbay.http.Version.paranoid=true
 wrapper.java.additional.3=-Dorg.mortbay.xml.XmlParser.NotValidating=true
 wrapper.java.additional.4=-Di2p.dir.base="$INSTALL_PATH"
 wrapper.java.additional.4.stripquotes=TRUE
+wrapper.java.additional.5=-Djava.net.preferIPv4Stack=true
 # Jetty says this is a security risk
 # Uncommenting this won't help as the router forces it to true
 # If you really need this, you have to set it in jetty.xml