Improve contenttype test source folder name eclipse-platform#219

Makes the org.eclipse.core.contenttype.tests use a different test
resources folder than the org.eclipse.core.expressions.tests project.

Contributes to
eclipse-platform#219

runtime/tests/org.eclipse.core.contenttype.tests/test.xml

@@ -22,11 +22,11 @@
 
   <!-- This target defines the tests that need to be run. -->
   <target name="suite">
-    <property name="expressions-folder" 
-              value="${eclipse-home}/expressions_folder"/>
-    <delete dir="${expressions-folder}" quiet="true"/>
+    <property name="contenttype-folder" 
+              value="${eclipse-home}/contenttype_folder"/>
+    <delete dir="${contenttype-folder}" quiet="true"/>
     <ant target="core-test" antfile="${library-file}" dir="${eclipse-home}">
-      <property name="data-dir" value="${expressions-folder}"/>
+      <property name="data-dir" value="${contenttype-folder}"/>
       <property name="plugin-name" value="${plugin-name}"/>
       <property name="classname" 
                 value="org.eclipse.core.internal.contenttype.tests.AllContenttypeTests"/>