tidying and a README about this part of the build

src/bindings/python/README.md

@@ -0,0 +1 @@
+The distutils script in this directory is meant to be invoked from scons. It will work if you build it here (`python setup.py build_ext`, optionally `--inplace` as scons invokes it), but we haven't done much testing of it outside the build system and don't really intend to. YHBW.

src/bindings/python/setup.py

@@ -7,7 +7,8 @@ import os, os.path, sys
 from distutils.core import setup, Extension
 
 invoked = os.getcwd()
-os.chdir(os.path.dirname(sys.argv[0]))
+if (os.path.dirname(sys.argv[0]) != ''):
+    os.chdir(os.path.dirname(sys.argv[0]))
 
 setup(name="hammer",
       version="0.9.0",
@@ -17,7 +18,6 @@ setup(name="hammer",
       description="""The Hammer parser combinator library""",
       ext_modules=[Extension('_hammer', ['hammer.i'],
                              swig_opts=['-DHAMMER_INTERNAL__NO_STDARG_H',
-                                        #('-outdir', os.getcwd()),
                                         '-I../../'],
                              define_macros=[('SWIG', None)],
                              depends=['allocator.h',