Add is_blank classifier

string/doc/quickref.xml

@@ -667,6 +667,13 @@
                             <functionname>is_space()</functionname>
                         </entry>
                     </row>
+                    <row>
+                        <entry>is_blank</entry>
+                        <entry>Recognize blanks</entry>
+                        <entry>
+                            <functionname>is_blank()</functionname>
+                        </entry>
+                    </row>
                     <row>
                         <entry>is_alnum</entry>
                         <entry>Recognize alphanumeric characters</entry>

string/test/predicate_test.cpp

@@ -138,7 +138,11 @@ void classification_test()
     TEST_CLASS( is_any_of( string("abc") ), "aaabbcc", "aaxb" );
     TEST_CLASS( is_any_of( "abc" ), "aaabbcc", "aaxb" );
     TEST_CLASS( is_from_range( 'a', 'c' ), "aaabbcc", "aaxb" );
-
+    
+#ifndef BOOST_NO_CXX11
+    TEST_CLASS( is_blank(), " \t", "\t \n\r" );
+#endif
+    
     TEST_CLASS( !is_classified(std::ctype_base::space), "...", "..\n\r\t " );
     TEST_CLASS( ( !is_any_of("abc") && is_from_range('a','e') ) || is_space(), "d e", "abcde" );