Build/PHPCS: improve check for superfluous whitespace in files

Apparently PSR2 turns a couple of the superfluous whitespace checks off.
This turns these back on.

There is one additional one turned off in PSR2 which I've left alone: the check for multiple blank lines in a row.
IMO, sometimes it's useful to use two blank lines to break up code for improved readability, so I'm quite happy to leave that one turned off.

phpcs.xml.dist

@@ -48,6 +48,18 @@
 		<exclude name="Squiz.ControlStructures.ControlSignature.SpaceAfterCloseBrace"/>
 	</rule>
 
+	<!-- PSR2 appears to ignore blank lines for superfluous whitespace and in several other places. Let's fix that. -->
+	<rule ref="Squiz.WhiteSpace.SuperfluousWhitespace">
+		<properties>
+			<property name="ignoreBlankLines" value="false"/>
+		</properties>
+	</rule>
+	<rule ref="Squiz.WhiteSpace.SuperfluousWhitespace.StartFile">
+		<severity>5</severity>
+	</rule>
+	<rule ref="Squiz.WhiteSpace.SuperfluousWhitespace.EndFile">
+		<severity>5</severity>
+	</rule>
 
     <!-- Use normalized array indentation. -->
     <rule ref="Generic.Arrays.ArrayIndent"/>