error-message: more detailed message for inaccessible files. (npm#18384)

PR-URL: npm#18384
Credit: @chrisjpatty
Reviewed-By: @zkat

lib/utils/error-message.js

@@ -23,8 +23,17 @@ function errorMessage (er) {
     case 'EACCES':
     case 'EPERM':
       short.push(['', er])
-      detail.push(['', ['\nPlease try running this command again as root/Administrator.'
-                ].join('\n')])
+      detail.push([
+        '',
+        [
+          '\nThe operation was rejected by your operating system.',
+          (process.platform === 'win32'
+            ? 'It\'s possible that the file was already in use (by a text editor or antivirus),\nor that you lack permissions to access it.'
+            : 'It is likely you do not have the permissions to access this file as the current user'),
+          '\nIf you believe this might be a permissions issue, please double-check the',
+          'permissions of the file and its containing directories, or try running',
+          'the command again as root/Administrator (though this is not recommended).'
+        ].join('\n')])
       break
 
     case 'ELIFECYCLE':