Generate a buildinfo property file with the current Git revision.

build.xml

@@ -5,9 +5,19 @@
     <mkdir dir="build" />
     <mkdir dir="build/classes" />
     <available property="has-res-jar" file="build/haven-res.jar" />
+    <available property="has-buildinfo" file="build/classes/buildinfo" />
     <available property="unpacked-lib" file="build/classes-lib" />
   </target>
 
+  <target name="buildinfo" depends="build-env" unless="has-buildinfo">
+    <exec executable="git" outputproperty="gitrev" failifexecutionfails="false">
+      <arg line="rev-parse HEAD" />
+    </exec>
+    <propertyfile file="build/classes/buildinfo">
+      <entry key="git-rev" value="${gitrev}" />
+    </propertyfile>
+  </target>
+
   <target name="haven-client" depends="build-env">
     <javac srcdir="src" destdir="build/classes" debug="on">
       <classpath>
@@ -40,7 +50,7 @@
     </unjar>
   </target>
 
-  <target name="jar" depends="haven-client,lib-classes">
+  <target name="jar" depends="haven-client,buildinfo,lib-classes">
     <jar destfile="build/haven.jar" update="true">
       <fileset dir="build/classes" />
       <fileset dir="build/classes-lib" />