[SCons] Allow compiler options which contain commas

Compiler options such as '-Wl,-z,rlero' were incorrectly being split into
multiple options by SCons. Compiler options must now be separated by spaces when
specified on the SCons command line.

Fixes #320

SConstruct

@@ -459,7 +459,8 @@ config_options = [
         'LD_LIBRARY_PATH,HOME'.""",
      defaults.env_vars),
     ('cxx_flags',
-     'Compiler flags passed to the C++ compiler only.',
+     """Compiler flags passed to the C++ compiler only. Separate multiple
+        options with spaces, e.g. cxx_flags='-g -Wextra -O3 --std=c++11'""",
      defaults.cxxFlags),
     ('cc_flags',
      'Compiler flags passed to both the C and C++ compilers, regardless of optimization level',

site_scons/buildutils.py

@@ -511,11 +511,11 @@ def formatOption(env, opt):
 
 def listify(value):
     """
-    Convert an option specified as a string to a list.  Allow both
-    comma and space as delimiters. Passes lists transparently.
+    Convert an option specified as a string to a list, using spaces as
+    delimiters. Passes lists transparently.
     """
     if isinstance(value, types.StringTypes):
-        return value.replace(',', ' ').split()
+        return value.split()
     else:
         # Already a sequence. Return as a list
         return list(value)