manual: add known issues entry about XOAUTH2 "invalid_grant"

- Split the manual asciidoc source file.
- Improve the Makefile to build the manuals.

Github-ref: https://github.com/OfflineIMAP/offlineimap/issues/374
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/imapserver.py

@@ -415,7 +415,8 @@ class IMAPServer(object):
               "failed:\n\t%s"% msg, OfflineImapError.ERROR.REPO)
 
         if not tried_to_authn:
-            methods = ", ".join([x[5:] for x in [x for x in imapobj.capabilities if x[0:5] == "AUTH="]])
+            methods = ", ".join([x[5:] for x in
+                [x for x in imapobj.capabilities if x[0:5] == "AUTH="]])
             raise OfflineImapError(u"Repository %s: no supported "
               "authentication mechanisms found; configured %s, "
               "server advertises %s"% (self.repos,