Fix a typo in Python setup error handling

[kankri]

If the setup.py script couldn't for some reason get a list of source files, it failed with the following exception:

>setup.py build
running build
running custom_build
running build_py
running build_clib
running custom_build_clib
Traceback (most recent call last):
  File "setup.py", line 266, in <module>
    main()
  File "setup.py", line 263, in main
    setup(**options)
  File "C:\Program Files (x86)\python27\lib\distutils\core.py", line 151, in setup
    dist.run_commands()
  File "C:\Program Files (x86)\python27\lib\distutils\dist.py", line 953, in run_commands
    self.run_command(cmd)
  File "C:\Program Files (x86)\python27\lib\distutils\dist.py", line 972, in run_command
    cmd_obj.run()
  File "setup.py", line 43, in run
    build.run(self)
  File "C:\Program Files (x86)\python27\lib\distutils\command\build.py", line 127, in run
    self.run_command(cmd_name)
  File "C:\Program Files (x86)\python27\lib\distutils\cmd.py", line 326, in run_command
    self.distribution.run_command(command)
  File "C:\Program Files (x86)\python27\lib\distutils\dist.py", line 972, in run_command
    cmd_obj.run()
  File "setup.py", line 95, in run
    build_clib.run(self)
  File "C:\Program Files (x86)\python27\lib\distutils\command\build_clib.py", line 116, in run
    self.build_libraries(self.libraries)
  File "setup.py", line 99, in build_libraries
    sources = self.get_source_files_for_lib(lib_name, build_info)
  File "setup.py", line 82, in get_source_files_for_lib
    raise DistutilsSetupError ("in 'libraries' option (library '%s'), 'sources' must be present and must be a list of source filenames") % lib_name
TypeError: unsupported operand type(s) for %: 'DistutilsSetupError' and 'str'

This can be demonstrated by setting the sources list empty:

diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -176,7 +176,7 @@
         libraries = [(
             'distorm3', dict(
             package='distorm3',
-            sources=get_sources,
+            sources=[],
             include_dirs=['src', 'include'],
             extra_compile_args=['/Ox', '/Ob1', '/Oy', '"/D WIN32"',
                                 '"/D DISTORM_DYNAMIC"', '"/D SUPPORT_64BIT_OFFSET"',

After the fix an error message is displayed instead of a stack trace:

>setup.py build
running build
running custom_build
running build_py
running build_clib
running custom_build_clib
error: in 'libraries' option (library 'distorm3'), 'sources' must be present and must be a list of source filenames