exchange: provide hint on how to disable clone bundles

If a clone bundle persistently fails to apply, users need a way to
disable it so they have a hope of the clone working. Change the hint for
the abort scenario to advertise the config option to disable clone
bundles.

mercurial/exchange.py

@@ -1637,8 +1637,10 b' def _maybeapplyclonebundle(pullop):'
         repo.ui.warn(_('falling back to normal clone\n'))
     else:
         raise error.Abort(_('error applying bundle'),
-                          hint=_('consider contacting the server '
-                                 'operator if this error persists'))
+                          hint=_('if this error persists, consider contacting '
+                                 'the server operator or disable clone '
+                                 'bundles via '
+                                 '"--config experimental.clonebundles=false"'))
 
 def parseclonebundlesmanifest(repo, s):
     """Parses the raw text of a clone bundles manifest.

tests/test-clonebundles.t

@@ -71,7 +71,7 b' Manifest file with invalid URL aborts'
   applying clone bundle from http://does.not.exist/bundle.hg
   error fetching bundle: [Errno -2] Name or service not known
   abort: error applying bundle
-  (consider contacting the server operator if this error persists)
+  (if this error persists, consider contacting the server operator or disable clone bundles via "--config experimental.clonebundles=false")
   [255]
 
 Server is not running aborts
@@ -81,7 +81,7 b' Server is not running aborts'
   applying clone bundle from http://localhost:$HGPORT1/bundle.hg
   error fetching bundle: [Errno 111] Connection refused
   abort: error applying bundle
-  (consider contacting the server operator if this error persists)
+  (if this error persists, consider contacting the server operator or disable clone bundles via "--config experimental.clonebundles=false")
   [255]
 
 Server returns 404
@@ -92,7 +92,7 b' Server returns 404'
   applying clone bundle from http://localhost:$HGPORT1/bundle.hg
   HTTP error fetching bundle: HTTP Error 404: File not found
   abort: error applying bundle
-  (consider contacting the server operator if this error persists)
+  (if this error persists, consider contacting the server operator or disable clone bundles via "--config experimental.clonebundles=false")
   [255]
 
 We can override failure to fall back to regular clone