fish.c: avoid "assignment discards qualifiers..." warning

* fish/fish.c (main): Cast-away-const.
* fish/fish.h (bad_cast): Define.  Safer than using an actual cast.

fish/fish.c

@@ -267,7 +267,7 @@ main (int argc, char *argv[])
         *p = '\0';
         mp->mountpoint = p+1;
       } else
-        mp->mountpoint = "/";
+        mp->mountpoint = bad_cast ("/");
       mp->device = optarg;
       mp->next = mps;
       mps = mp;

fish/fish.h

@@ -106,4 +106,10 @@ extern char *try_tilde_expansion (char *path);
   "reopen",				\
   "time"
 
+static inline char *
+bad_cast (char const *s)
+{
+  return (char *) s;
+}
+
 #endif /* FISH_H */