change checkstyle default severity to error

[Christian Thalinger]

Could we change the checkstyle default severity to error?  It would make it easier to write a Mercurial commit hook.

-- Chris

diff --git a/graal/com.oracle.graal.graph/.checkstyle_checks.xml b/graal/com.oracle.graal.graph/.checkstyle_checks.xml
--- a/graal/com.oracle.graal.graph/.checkstyle_checks.xml
+++ b/graal/com.oracle.graal.graph/.checkstyle_checks.xml
@@ -9,7 +9,7 @@
     Description: none
 -->
 <module name="Checker">
-  <property name="severity" value="warning"/>
+  <property name="severity" value="error"/>
   <module name="TreeWalker">
     <property name="tabWidth" value="4"/>
     <module name="FileContentsHolder"/>