add positive time span validator

svn path=/trunk/mcs/; revision=52168

mcs/class/System.Configuration/System.Configuration.dll.sources

@@ -76,6 +76,7 @@ System.Configuration/LongValidator.cs
 System.Configuration/LongValidatorAttribute.cs
 System.Configuration/NameValueConfigurationCollection.cs
 System.Configuration/NameValueConfigurationElement.cs
+System.Configuration/PositiveTimeSpanValidator.cs
 System.Configuration/PropertyInformation.cs
 System.Configuration/PropertyInformationCollection.cs
 System.Configuration/PropertyValueOrigin.cs

mcs/class/System.Configuration/System.Configuration_test.dll.sources

@@ -9,6 +9,7 @@ System.Configuration/IntegerValidatorTest.cs
 System.Configuration/KeyValueConfigurationCollectionTest.cs
 System.Configuration/KeyValueConfigurationElementTest.cs
 System.Configuration/LongValidatorTest.cs
+System.Configuration/PositiveTimeSpanValidatorTest.cs
 System.Configuration/RegexStringValidatorTest.cs
 System.Configuration/StringValidatorTest.cs
 System.Configuration/SubclassTypeValidatorTest.cs