svn: Ignore the content length header from response, fixes #4112

In case of compressed responses from apache(mod_dav_svn) we can not
use the Content-Length header in our own response. The content is
automatically decompressed by the requests library and therefore
the content length differs.

This results in errors when doing e.g. a svn checkout:
"svn: E120106: ra_serf: The server sent a truncated HTTP response body."

rhodecode/lib/middleware/simplesvn.py

@@ -30,7 +30,7 b' from rhodecode.lib.utils import is_valid'
 class SimpleSvnApp(object):
     IGNORED_HEADERS = [
         'connection', 'keep-alive', 'content-encoding',
-        'transfer-encoding']
+        'transfer-encoding', 'content-length']
 
     def __init__(self, config):
         self.config = config