Don't scan python bindings until the everything.h file to be scanned is generated. Closes #288.

bindings/python/wscript

@@ -223,6 +223,7 @@ __dummy_function_to_force_template_instantiation (Ptr<Object> obj, TypeId typeId
     return 0
 
 
+
 class all_ns3_headers_taskgen(Object.task_gen):
     """Generates a 'everything.h' header file that includes some/all public ns3 headers.
     This single header file is to be parsed only once by gccxml, for greater efficiency.
@@ -293,6 +294,33 @@ def get_modules_and_headers():
     return retval
 
 
+
+class PythonScanTask(Task.TaskBase):
+    """Uses gccxml to scan the file 'everything.h' and extract API definitions.
+    """
+    def __init__(self, curdirnode, env):
+        self.m_display = 'python-scan'
+        self.prio = 5 # everything.h has prio 4
+        super(PythonScanTask, self).__init__()
+        self.curdirnode = curdirnode
+        self.env = env
+
+    def run(self):
+        #print "Rescanning the python bindings..."
+        argv = [
+            self.env['PYTHON'],
+            os.path.join(self.curdirnode.abspath(), 'ns3modulescan.py'), # scanning script
+            self.curdirnode.find_dir('../..').abspath(self.env), # include path (where the ns3 include dir is)
+            self.curdirnode.find_build('everything.h').abspath(self.env),
+            os.path.join(self.curdirnode.abspath(), 'ns3modulegen_generated.py'), # output file
+            ]
+        scan = subprocess.Popen(argv, stdin=subprocess.PIPE)
+        scan.stdin.write(repr(get_modules_and_headers()))
+        scan.stdin.close()
+        if scan.wait():
+            raise SystemExit(1)
+
+
 def build(bld):
     if Params.g_options.python_disable:
         return
@@ -307,22 +335,7 @@ def build(bld):
     if Params.g_options.python_scan:
         if not env['ENABLE_PYTHON_SCANNING']:
             Params.fatal("Cannot re-scan python bindings: (py)gccxml not available")
-        print "Rescanning the python bindings..."
-        curdir = bld.m_curdirnode.abspath()
-        argv = [
-            env['PYTHON'],
-            os.path.join(curdir, 'ns3modulescan.py'), # scanning script
-            bld.m_curdirnode.find_dir('../..').abspath(env), # include path (where the ns3 include dir is)
-            bld.m_curdirnode.find_build('everything.h').abspath(env),
-            os.path.join(curdir, 'ns3modulegen_generated.py'), # output file
-            ]
-        scan = subprocess.Popen(argv, stdin=subprocess.PIPE)
-        scan.stdin.write(repr(get_modules_and_headers()))
-        scan.stdin.close()
-        if scan.wait():
-            raise SystemExit(1)
-        print "Rescanning the python bindings done."
-        raise SystemExit
+        PythonScanTask(bld.m_curdirnode, env)
 
     ## Get a list of scanned modules; the set of scanned modules
     ## may be smaller than the set of all modules, in case a new