Ensure SOURCES.txt references itself even the first time it is generated

(i.e., when it didn't exist prior to egg_info being run).

--HG--
branch : setuptools
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/trunk/setuptools%4043295

setuptools/command/egg_info.py

@@ -218,6 +218,8 @@ class manifest_maker(sdist):
 
     def run(self):
         self.filelist = FileList()
+        if not os.path.exists(self.manifest):
+            self.write_manifest()   # it must exist so it'll get in the list
         self.filelist.findall()
         self.add_defaults()
         if os.path.exists(self.template):
@@ -242,8 +244,6 @@ class manifest_maker(sdist):
 
 
 
-
-
     def add_defaults(self):
         sdist.add_defaults(self)
         self.filelist.append(self.template)