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/progdlg.h

@@ -167,7 +167,7 @@ public:
 
     /**
         Changes the maximum value of the progress meter given in the constructor.
-        This function can only be called (with a positive value) if the value passed 
+        This function can only be called (with a positive value) if the value passed
         in the constructor was positive.
 
         @since 2.9.1