Polish the migration guide

- Added missing <para> tags to the JDiff reports section.

 - Converted tabs to spaces.

src/reference/docbook/migration-3.2.xml

@@ -148,6 +148,7 @@
 
     <section xml:id="migration-3.2-api-changes">
       <title>JDiff reports</title>
+      <para>
       Select JDiff reports are now being published to provide users with a convenient
       means of understanding what's changed between versions. Going forward these will be
       published between each minor version, e.g. from 3.1.3.RELEASE to 3.1.4.RELEASE; from
@@ -157,6 +158,7 @@
       and/or RC for users who are tracking next-generation development, e.g.
       <link xl:href="http://static.springsource.org/spring-framework/docs/3.2.0.RC2_to_3.2.0.RELEASE">
       3.2.0.RC2 to 3.2.0.RELEASE</link>.
+      </para>
     </section>
 
     <section xml:id="migration-3.2-removals-and-deprecations">