Unify encoding name normalization

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/util/CharsetMapping.java

@@ -26,7 +26,7 @@ public static Charset getCharset(String encoding) {
     }
 
     private static String normalize(String encoding) {
-        return encoding.toLowerCase(Locale.ENGLISH).replaceAll("\\W+", "_");
+        return encoding.toLowerCase(Locale.ENGLISH).replaceAll("[^\\w.]+", "_");
     }
 
     private static Charset getJavaCharset(String name) {

graalpython/lib-graalpython/_codecs.py

@@ -50,8 +50,22 @@ def register(search_function):
     __codec_search_path__.append(search_function)
 
 
-def __normalizestring(string):
-    return string.replace(' ', '-').lower()
+def __normalizestring(encoding):
+    # Copied from encodings.normalize_encoding + added lowercasing
+    if isinstance(encoding, bytes):
+        encoding = ascii_decode(encoding)[0]
+
+    chars = []
+    punct = False
+    for c in encoding:
+        if c.isalnum() or c == '.':
+            if punct and chars:
+                chars.append('_')
+            chars.append(c.lower())
+            punct = False
+        else:
+            punct = True
+    return ''.join(chars)
 
 
 @__graalpython__.builtin