dispatch: show empty filename in OSError aborts

Mercurial would sometimes exit with:
  abort: No such file or directory
where str of the actual OSError exception was the more helpful:
  [Errno 2] No such file or directory: ''

The exception will now always show the filename and quote it:
  abort: No such file or directory: ''

mercurial/dispatch.py

@@ -183,8 +183,8 b' def _runcatch(req):'
         else:
             raise
     except OSError, inst:
-        if getattr(inst, "filename", None):
-            ui.warn(_("abort: %s: %s\n") % (inst.strerror, inst.filename))
+        if getattr(inst, "filename", None) is not None:
+            ui.warn(_("abort: %s: '%s'\n") % (inst.strerror, inst.filename))
         else:
             ui.warn(_("abort: %s\n") % inst.strerror)
     except KeyboardInterrupt:

tests/test-audit-path.t

@@ -86,7 +86,7 b' attack /tmp/test'
   $ hg manifest -r4
   /tmp/test
   $ hg update -Cr4
-  abort: *: $TESTTMP/target//tmp/test (glob)
+  abort: *: '$TESTTMP/target//tmp/test' (glob)
   [255]
 
   $ cd ..

tests/test-clone.t

@@ -558,7 +558,7 b' Inaccessible destination'
   $ hg init b
   $ cd b
   $ hg clone . ../a
-  abort: Permission denied: ../a
+  abort: Permission denied: '../a'
   [255]
   $ cd ..
   $ chmod 700 a

tests/test-convert.t

@@ -316,7 +316,7 b' conversion to dir without permissions sh'
   $ chmod 000 bogusdir
 
   $ hg convert a bogusdir
-  abort: Permission denied: bogusdir
+  abort: Permission denied: 'bogusdir'
   [255]
 
 user permissions should succeed

tests/test-dispatch.t

@@ -46,6 +46,12 b' Missing arg:'
 
   $ cd "$TESTTMP"
 
+OSError ... and with filename even when it is empty
+
+  $ hg -R a archive ''
+  abort: No such file or directory: ''
+  [255]
+
 #if no-outer-repo
 
 No repo: