wireproto: add out-of-band error class to allow remote repo to report errors Older clients will still print the provided error message and not much else: over ssh, this will be each line prefixed with 'remote: ' in addition to an "abort: unexpected response: '\n'"; over http, this will be the '---%<---' banners in addition to the 'does not appear to be a repository' message. Currently, clients with this patch will display 'abort: remote error:\n' and the provided error text, but it is trivial to style the error text however is deemed appropriate.

--- a/mercurial/dispatch.py	Wed Aug 03 16:41:14 2011 -0500
+++ b/mercurial/dispatch.py	Tue Aug 02 15:21:10 2011 -0400
@@ -123,6 +123,9 @@
         else:
             ui.warn(_("hg: %s\n") % inst.args[1])
             commands.help_(ui, 'shortlist')
+    except error.OutOfBandError, inst:
+        ui.warn("abort: remote error:\n")
+        ui.warn(''.join(inst.args))
     except error.RepoError, inst:
         ui.warn(_("abort: %s!\n") % inst)
         if inst.hint: