[IMP] Cleanup and refactoring of exception handling

Unify and refactor exception handling in framework and addons.

The generic `except_osv` is now deprecated, and replaced by more specialized exception subtypes:
 - `UserError` (renamed from Warning, as it conflicts with the built-in `Warning`) raised when a non-technical error occurs during a business operation. It could be a missing information in the data provided by the user, or a misconfiguration.
 - `AccessError`: raised when any operation is denied because the user conducting it does not have the required access rights.
 - `AccessDenied`: raised when an operation that requires authenticated access is attempted via an unauthenticated request.
 - `MissingError`: raised when an operation is attempted on a record that does not exist.
 - `ValidationError`: raised when an operation violates a SQL or Python constraint.
 - All other exceptions are internal errors due to a system problem or bug, and raised untouched to the client-side, which should display a traceback.

All exceptions take a single message argument.

The `test_exceptions` module has been updated to showcase both new and old (deprecated) exceptions.

A great many old `except_osv` had a useless title with "Error!" or "Warning", those have been removed, as this is handled by the client-side widget that displays the messages.

This commit introduces a more consistent policy for logging errors and warnings:
 - All messages that do not require administrator attention should be logged at INFO level or lower. This includes all errors that are notified to the user in a friendly manner, even for access right problems or validation errors during business operations.
 - All messages that indicate a likely misconfiguration or malicious use by the users should be logged at WARNING level, as they typically require administrator attention.
 - All other unhandled internal errors cannot typically be handled by the user and should be logged at ERROR or higher level, as they require immediate administrator attention.

1 files changed, 1 insertions, 2 deletions

diff --git a/openerp/modules/loading.py b/openerp/modules/loading.py
index fb52de60f06..33475493115 100644
--- a/openerp/modules/loading.py
+++ b/openerp/modules/loading.py
@@ -36,7 +36,6 @@ import openerp.modules.db
 import openerp.modules.graph
 import openerp.modules.migration
 import openerp.modules.registry
-import openerp.osv as osv
 import openerp.tools as tools
 from openerp import SUPERUSER_ID
 
@@ -297,7 +296,7 @@ def load_modules(db, force_demo=False, status=None, update_module=False):
         graph.add_module(cr, 'base', force)
         if not graph:
             _logger.critical('module base cannot be loaded! (hint: verify addons-path)')
-            raise osv.osv.except_osv(_('Could not load base module'), _('module base cannot be loaded! (hint: verify addons-path)'))
+            raise ImportError('Module `base` cannot be loaded! (hint: verify addons-path)')
 
         # processed_modules: for cleanup step after install
         # loaded_modules: to avoid double loading