Constify the isValid() method (backported around one week ago)

Will fix in trunk on monday, but I have to do this before tagging (tomorrow) here in branch.  

Thanks to André for noticing that.

CCMAIL: Woebbeking@kde.org
CCMAIL: kde-core-devel@kde.org

svn path=/branches/KDE/4.2/kdelibs/; revision=960777

runnercontext.cpp

@@ -208,7 +208,7 @@ QString RunnerContext::mimeType() const
     return d->mimeType;
 }
 
-bool RunnerContext::isValid()
+bool RunnerContext::isValid() const
 {
     // if our qptr is dirty, we aren't useful anymore
     return (d->q != &(d->s_dummyContext));

runnercontext.h

@@ -119,7 +119,7 @@ class PLASMA_EXPORT RunnerContext : public QObject
          * to avoid unecessary processing in runners that may run for an extended
          * period (as measured in 10s of ms) and therefore improve the user experience. @since 4.2.3
          */
-        bool isValid();
+        bool isValid() const;
 
 
          /**