Check for 'SORT' capability in _sort(). Fix style and wording.

lib/imap.js

@@ -789,22 +789,24 @@ ImapConnection.prototype._sort = function(which, sorts, options, cb) {
   if (this._state.status !== STATES.BOXSELECTED)
     throw new Error('No mailbox is currently selected');
   if (!Array.isArray(sorts) || !sorts.length)
-    throw new Error('Expected array with at least on criterion for sort criteria');
+    throw new Error('Expected array with at least one sort criteria');
   if (!Array.isArray(options))
     throw new Error('Expected array for search options');
+  if (!this._serverSupports('SORT'))
+    return cb(new Error('Sorting is not supported on the server'));
 
   var criteria = sorts.map(function(criterion) {
-    if(typeof criterion !== 'string')
+    if (typeof criterion !== 'string')
       throw new Error('Unexpected sort criterion data type. '
                       + 'Expected string. Got: ' + typeof criteria);
 
     var modifier = '';
-    if(criterion.charAt(0) === '!') {
+    if (criterion.charAt(0) === '!') {
       modifier = 'REVERSE ';
       criterion = criterion.substring(1);
     }
     criterion = criterion.toUpperCase();
-    switch(criterion) {
+    switch (criterion) {
       case 'ARRIVAL':
       case 'CC':
       case 'DATE':
@@ -814,7 +816,7 @@ ImapConnection.prototype._sort = function(which, sorts, options, cb) {
       case 'TO':
         break;
       default:
-        throw new Error('Unexpected sort criterion: ' + criterion);
+        throw new Error('Unexpected sort criteria: ' + criterion);
     }
 
     return modifier + criterion;