Trimming MVEL scripts before compiling them.

This bypasses an issue with MVEL error handling why can go into an infinite loop in some edge cases. More info here: http://jira.codehaus.org/browse/MVEL-292

Closes elastic#3168

src/main/java/org/elasticsearch/script/mvel/MvelScriptEngineService.java

@@ -82,7 +82,7 @@ public String[] extensions() {
 
     @Override
     public Object compile(String script) {
-        return MVEL.compileExpression(script, new ParserContext(parserConfiguration));
+        return MVEL.compileExpression(script.trim(), new ParserContext(parserConfiguration));
     }
 
     @Override