Update PEP 7. All C files should now use 4-space indents.

pep-0007.txt

@@ -46,13 +46,7 @@ C dialect
 
 Code lay-out
 
-    - Use single-tab indents, where a tab is worth 8 spaces, in files
-      that already use tabs.  In new source files, and the few files
-      that were created after this rule was introduced, use 4-space
-      indents and no tabs at all.
-
-      At some point, the whole codebase may be converted to use only
-      4-space indents.
+    - Use 4-space indents and no tabs at all.
 
     - No line should be longer than 79 characters.  If this and the
       previous rule together don't give you enough room to code, your