Declare several parameters/variables constant

Add the "const" keyword to parameters and variables that are never
modified. Most of these were spotted by "-Wwrite-strings".

We cast the second parameter to execvp() explicitly as it expects a
"char *const[]" where it should expect a "const char *const[]"
(according to the documentation, this is due to compatibility reasons).
This should be changed once we come up with a better solution.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/wins.c

@@ -620,9 +620,9 @@ wins_unprepare_external (void)
  * file.
  */
 void
-wins_launch_external (char *file, char *cmd)
+wins_launch_external (const char *file, const char *cmd)
 {
-  char *arg[] = { cmd, file, NULL };
+  const char *arg[] = { cmd, file, NULL };
   int pid;
 
   wins_prepare_external ();