And now we fix src/gwt/build.xml since java's user preference class is
braindead and insists on writing where it is not allowed.
much thanks to http://www.allaboutbalance.com/articles/disableprefs/

diff --git a/src/gwt/build.xml b/src/gwt/build.xml
index e7d2418..ae3a331 100644
--- a/src/gwt/build.xml
+++ b/src/gwt/build.xml
@@ -25,6 +25,7 @@
    <property name="gwt.extra.args" value=""/>
    <property name="gwt.main.module" value="org.rstudio.studio.RStudio"/>
    <property name="ace.bin" value="src/org/rstudio/studio/client/workbench/views/source/editors/text/ace"/>
+   <property environment="env"/>
 
    <path id="project.class.path">
       <pathelement location="bin"/>
@@ -109,6 +110,7 @@
          </classpath>
          <!-- add jvmarg -Xss16M or similar if you see a StackOverflowError -->
          <jvmarg value="-Xmx1024M"/>
+         <jvmarg value="-Djava.util.prefs.userRoot=${env.T}"/>
          <arg value="-war"/>
          <arg value="www"/>
          <arg value="-localWorkers"/>