Add plugin.properties required by net4j at runtime.

tools.descartes.prisma.releng.standalone/assemble/plugin.properties

+# This file is required by net4j so that it can determine its base path.
\ No newline at end of file

tools.descartes.prisma.releng.standalone/assemble/standalone.xml

@@ -15,5 +15,12 @@
 				<include>**/*</include>
 			</includes>
 		</fileSet>
+		<fileSet>
+			<directory>assemble</directory>
+			<outputDirectory>.</outputDirectory>
+			<includes>
+				<include>plugin.properties</include>
+			</includes>
+		</fileSet>
 	</fileSets>
 </assembly>
\ No newline at end of file