Bug 860: waf dies while executing ns3header task in case of parallel jobs.

src/wscript

@@ -11,6 +11,11 @@ import Options
 import Build
 import Utils
 
+try:
+    set
+except NameError:
+    from sets import Set as set # Python 2.3 fallback
+
 all_modules = (
     'core',
     'common',
@@ -140,7 +145,7 @@ class ns3header_taskgen(TaskGen.task_gen):
         ns3_dir_node = self.bld.path.find_dir("ns3")
         if self.sub_dir is not None:
             ns3_dir_node = ns3_dir_node.find_dir(self.sub_dir)
-        for filename in self.to_list(self.source):
+        for filename in set(self.to_list(self.source)):
             src_node = self.path.find_resource(filename)
             if src_node is None:
                 raise Utils.WafError("source ns3 header file %s not found" % (filename,))
@@ -238,7 +243,7 @@ class ns3moduleheader_taskgen(TaskGen.task_gen):
                 if ns3headers.module != self.module:
                     continue
                 found_the_module = True
-                for source in ns3headers.to_list(ns3headers.source):
+                for source in set(ns3headers.to_list(ns3headers.source)):
                     source = os.path.basename(source)
                     node = ns3_dir_node.find_or_declare(os.path.basename(source))
                     if node is None: