[changed] Split integer(), remove transform

integer() no longer adds a type coercion, and now only validates the
input is an integer.

the truncate() method has been added to coerce inputs to integers, via
truncation (the same behavior as integer before)

src/number.js

@@ -69,18 +69,25 @@ inherits(NumberSchema, MixedSchema, {
   },
 
   integer(msg) {
-    msg = msg || locale.integer
+    msg = msg || locale.integer;
 
-    return this
-      .transform(value => !isAbsent(value) ? (value | 0) : value)
-      .test('integer', msg, isInteger)
+    return this.test('integer', msg, isInteger)
+  },
+
+  truncate() {
+    return this.transform(value =>
+      !isAbsent(value) ? (value | 0) : value)
   },
 
   round(method) {
-    var avail = ['ceil', 'floor', 'round']
+    var avail = ['ceil', 'floor', 'round', 'trunc']
     method = (method && method.toLowerCase()) || 'round'
 
-    if( avail.indexOf(method.toLowerCase()) === -1 )
+    // this exists for symemtry with the new Math.trunc
+    if (method === 'trunc')
+      return this.truncate()
+
+    if (avail.indexOf(method.toLowerCase()) === -1)
       throw new TypeError('Only valid options for round() are: ' + avail.join(', '))
 
     return this.transform(value => !isAbsent(value) ? Math[method](value) : value)