Fail the build script if generation of AMQP.java

or AMQPImpl.java fails. Print error message.

Author: Hubert Plociniczak

build.xml

@@ -44,17 +44,37 @@
   <target name="amqp-generate" depends="amqp-generate-check"
     unless="amqp.generate.notRequired" description="generate AMQP.java and AMQImpl.java from AMQP spec">
     <mkdir dir="${src.generated}/com/rabbitmq/client/"/>
-    <exec dir="." executable="python" output="${src.generated}/com/rabbitmq/client/AMQP.java">
+    <exec dir="." executable="python"
+          output="${src.generated}/com/rabbitmq/client/AMQP.java"
+    	  errorproperty="amqp.generate.error1"
+          resultproperty="amqp.generate.result1">
       <arg line="codegen.py"/>
       <arg line="header"/>
       <arg line="${AMQP_SPEC_JSON_PATH}"/>
     </exec>
+  	<fail message="Generation of AMQP.java failed with message:${line.separator}${amqp.generate.error1}">
+        <condition>
+            <not>
+                <equals arg1="${amqp.generate.result1}" arg2="0" />
+            </not>
+        </condition>
+    </fail>
     <mkdir dir="${src.generated}/com/rabbitmq/client/impl"/>
-    <exec dir="." executable="python" output="${src.generated}/com/rabbitmq/client/impl/AMQImpl.java">
+    <exec dir="." executable="python"
+          output="${src.generated}/com/rabbitmq/client/impl/AMQImpl.java"
+          errorproperty="amqp.generate.error2"
+          resultproperty="amqp.generate.result2">
       <arg line="codegen.py"/>
       <arg line="body"/>
       <arg line="${AMQP_SPEC_JSON_PATH}"/>
     </exec>
+  	<fail message="Generation of AMQPImpl.java failed with message:${line.separator}${amqp.generate.error2}">
+        <condition>
+            <not>
+                <equals arg1="${amqp.generate.result2}" arg2="0" />
+            </not>
+        </condition>
+  	</fail>
   </target>
 
   <target name="build" depends="amqp-generate">