Replace INSTALL_LIB on installation.

This restores code removed in r28342, which rewrites sys.path to include
the directory in which the Zenmap modules are installed. This is needed
to run the program without changes to PYTHONPATH when the installation
directory is not among the Python interpreter's default search paths.
(/usr/local/lib/python2.7/site-packages/ or a user's home directory are
common cases.) A difference is that now we make sure that the directory
we are adding is not writable by any other users, to avoid installation
mistakes like Debian bug #663217.

zenmap/setup.py

@@ -205,6 +205,7 @@ class my_install(install):
         install.run(self)
 
         self.set_perms()
+        self.set_modules_path()
         self.fix_paths()
         self.create_uninstaller()
         self.write_installed_files()
@@ -306,6 +307,30 @@ for dir in dirs:
         mode = ((os.stat(uninstaller_filename)[ST_MODE]) | 0555) & 07777
         os.chmod(uninstaller_filename, mode)
 
+    def set_modules_path(self):
+        app_file_name = os.path.join(self.install_scripts, APP_NAME)
+        # Find where the modules are installed. distutils will put them in
+        # self.install_lib, but that path can contain the root (DESTDIR), so we
+        # must strip it off if necessary.
+        modules_dir = self.install_lib
+        if self.root is not None:
+            modules_dir = path_strip_prefix(modules, self.root)
+
+        app_file = open(app_file_name, "r")
+        lines = app_file.readlines()
+        app_file.close()
+
+        for i in range(len(lines)):
+            if re.match(r'^INSTALL_LIB =', lines[i]):
+                lines[i] = "INSTALL_LIB = %s\n" % repr(modules_dir)
+                break
+        else:
+            raise ValueError("INSTALL_LIB replacement not found in %s" % app_file_name)
+
+        app_file = open(app_file_name, "w")
+        app_file.writelines(lines)
+        app_file.close()
+
     def set_perms(self):
         re_bin = re.compile("(bin|\.sh)")
         for output in self.get_installed_files():