fix: suggest --source instead of --rev on empty revset

`--source` is the recommended flag for regular users (`--rev` is
available for advanced users).

Differential Revision: https://phab.mercurial-scm.org/D9224

hgext/fix.py

@@ -439,7 +439,7 b' def getrevstofix(ui, repo, opts):'
         raise error.Abort(b'unresolved conflicts', hint=b"use 'hg resolve'")
     if not revs:
         raise error.Abort(
-            b'no changesets specified', hint=b'use --rev or --working-dir'
+            b'no changesets specified', hint=b'use --source or --working-dir'
         )
     return revs
 

tests/test-fix.t

@@ -246,15 +246,15 b' There is no default behavior in the abse'
 
   $ hg fix
   abort: no changesets specified
-  (use --rev or --working-dir)
+  (use --source or --working-dir)
   [255]
   $ hg fix --whole
   abort: no changesets specified
-  (use --rev or --working-dir)
+  (use --source or --working-dir)
   [255]
   $ hg fix --base 0
   abort: no changesets specified
-  (use --rev or --working-dir)
+  (use --source or --working-dir)
   [255]
 
 Fixing a public revision isn't allowed. It should abort early enough that