Fix inconsistency with the email field of the user table. It always was...

Fix inconsistency with the email field of the user table. It always was nullable in all previous versions, there's no reason to change that now

htdocs/lib/db/install.xml

@@ -96,7 +96,7 @@
                 <FIELD NAME="lastname" TYPE="text" NOTNULL="false"/>
                 <FIELD NAME="studentid" TYPE="text" NOTNULL="false"/>
                 <FIELD NAME="preferredname" TYPE="text" NOTNULL="false"/>
-                <FIELD NAME="email" TYPE="char" LENGTH="255" NOTNULL="true" />
+                <FIELD NAME="email" TYPE="char" LENGTH="255" NOTNULL="false"/>
                 <!-- This field should be foreign keyed to the artefact table, however the
                 artefact table already has a key to this table, and XMLDB isn't smart enough
                 to create the tables first, then the keys. -->