errors: use detailed exit code when trying to merge file outside narrowspec

Differential Revision: https://phab.mercurial-scm.org/D11827

mercurial/merge.py

@@ -542,7 +542,7 b' def _filternarrowactions(narrowmatch, br'
                 hint=_(b'merging in the other direction may work'),
             )
         else:
-            raise error.Abort(
+            raise error.StateError(
                 _(b'conflict in file \'%s\' is outside narrow clone') % f
             )
 

tests/test-narrow-merge.t

@@ -101,4 +101,4 b' Refuses merge of conflicting outside cha'
   $ hg merge 'desc("conflicting outside/f1")'
   abort: conflict in file 'outside/f1' is outside narrow clone (flat !)
   abort: conflict in file 'outside/' is outside narrow clone (tree !)
-  [255]
+  [20]

tests/test-narrow-rebase.t

@@ -96,4 +96,4 b' Rebase interrupts on conflicting changes'
   $ hg rebase -d 'desc("modify outside/f1")'
   rebasing 4:707c035aadb6 "conflicting outside/f1"
   abort: conflict in file 'outside/f1' is outside narrow clone
-  [255]
+  [20]