Allow fenced_code to be configurable in subclasses.

Not sure why I was using global variables here. Anyway. Fixed now.
Thanks to Andrew for pointing it out.

markdown/extensions/fenced_code.py

@@ -80,13 +80,6 @@
 from .codehilite import CodeHilite, CodeHiliteExtension
 import re
 
-# Global vars
-FENCED_BLOCK_RE = re.compile( \
-    r'(?P<fence>^(?:~{3,}|`{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)?[ ]*\n(?P<code>.*?)(?<=\n)(?P=fence)[ ]*$',
-    re.MULTILINE|re.DOTALL
-    )
-CODE_WRAP = '<pre><code%s>%s</code></pre>'
-LANG_TAG = ' class="%s"'
 
 class FencedCodeExtension(Extension):
 
@@ -100,6 +93,12 @@ def extendMarkdown(self, md, md_globals):
 
 
 class FencedBlockPreprocessor(Preprocessor):
+    FENCED_BLOCK_RE = re.compile( \
+        r'(?P<fence>^(?:~{3,}|`{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)?[ ]*\n(?P<code>.*?)(?<=\n)(?P=fence)[ ]*$',
+        re.MULTILINE|re.DOTALL
+    )
+    CODE_WRAP = '<pre><code%s>%s</code></pre>'
+    LANG_TAG = ' class="%s"'
 
     def __init__(self, md):
         super(FencedBlockPreprocessor, self).__init__(md)
@@ -121,11 +120,11 @@ def run(self, lines):
 
         text = "\n".join(lines)
         while 1:
-            m = FENCED_BLOCK_RE.search(text)
+            m = self.FENCED_BLOCK_RE.search(text)
             if m:
                 lang = ''
                 if m.group('lang'):
-                    lang = LANG_TAG % m.group('lang')
+                    lang = self.LANG_TAG % m.group('lang')
 
                 # If config is not empty, then the codehighlite extension
                 # is enabled, so we call it to highlite the code
@@ -140,7 +139,7 @@ def run(self, lines):
 
                     code = highliter.hilite()
                 else:
-                    code = CODE_WRAP % (lang, self._escape(m.group('code')))
+                    code = self.CODE_WRAP % (lang, self._escape(m.group('code')))
 
                 placeholder = self.markdown.htmlStash.store(code, safe=True)
                 text = '%s\n%s\n%s'% (text[:m.start()], placeholder, text[m.end():])