Remove all trailing spaces

No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.

This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.

interface/wx/thread.h

@@ -1224,7 +1224,7 @@ public:
         of detached threads.
 
         This function can only be called from another thread context.
-        
+
         Finally, note that once a thread has completed and its Entry() function
         returns, you cannot call Run() on it again (an assert will fail in debug
         builds or @c wxTHREAD_RUNNING will be returned in release builds).