Throw OfflineImapErrors rather than weird Exceptions

When misconfiguring OLI, e.g. by specifying a repository name that was
not configured anywhere, we would bomb out with cryptic "NoSectionError".
Throw OfflineImapError that explains what has happened. We still need to
avoid throwing exceptions with Tracebacks here though.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

Changelog.rst

@@ -17,6 +17,7 @@ WIP (add new stuff for the next release)
   necessary, it might have been breaking things. (J. Wiegley)
 * Improve regex that could lead to 'NoneType' object has no attribute 'group'
   (D. Franke)
+* Improved error throwing on repository misconfiguration
 
 OfflineIMAP v6.5.4 (2012-06-02)
 ===============================

offlineimap/repository/__init__.py

@@ -15,10 +15,17 @@
 #    along with this program; if not, write to the Free Software
 #    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 
+try:
+    from configparser import NoSectionError
+except ImportError: #python2
+    from ConfigParser import NoSectionError
+
 from offlineimap.repository.IMAP import IMAPRepository, MappedIMAPRepository
 from offlineimap.repository.Gmail import GmailRepository
 from offlineimap.repository.Maildir import MaildirRepository
 from offlineimap.repository.LocalStatus import LocalStatusRepository
+from offlineimap.error import OfflineImapError
+
 
 class Repository(object):
     """Abstract class that returns the correct Repository type
@@ -47,17 +54,26 @@ class Repository(object):
             return LocalStatusRepository(name, account)
 
         else:
-            raise ValueError("Request type %s not supported" % reqtype)
+            errstr = "Repository type %s not supported" % reqtype
+            raise OfflineImapError(errstr, OfflineImapError.ERROR.REPO)
 
+        # Get repository type
         config = account.getconfig()
+        try:
             repostype = config.get('Repository ' + name, 'type').strip()
+        except NoSectionError as e:
+            errstr = ("Could not find section '%s' in configuration. Required "
+                      "for account '%s'." % ('Repository %s' % name, account))
+            raise OfflineImapError(errstr, OfflineImapError.ERROR.REPO)
+
         try:
             repo = typemap[repostype]
         except KeyError:
-            raise ValueError("'%s' repository not supported for %s repositories"
-                             "." % (repostype, reqtype))
-        return repo(name, account)
+            errstr = "'%s' repository not supported for '%s' repositories." \
+                     % (repostype, reqtype)
+            raise OfflineImapError(errstr, OfflineImapError.ERROR.REPO)
 
+        return repo(name, account)
 
     def __init__(self, account, reqtype):
         """Load the correct Repository type and return that. The