maint: accommodate gcc's -Wstrict-overflow option

* src/factor.c (factor_using_pollard_rho): Change type of "i"
to unsigned to avoid warning from gcc's -Wstrict-overflow.
* src/expr.c: Use an unsigned intermediate.
* src/dircolors.c (main): Reorder operations to avoid the risk of
pointer overflow.
* src/tr.c (squeeze_filter): Change NOT_A_CHAR from an anonymous
"enum" to an "int", to avoid this warning:
tr.c:1624:10: error: assuming signed overflow does not occur when
  simplifying conditional to constant [-Werror=strict-overflow]
* src/pr.c (main): Make index "i" unsigned.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/factor.c b/src/factor.c
index 3354a4d5b..27843201c 100644
--- a/src/factor.c
+++ b/src/factor.c
@@ -160,7 +160,7 @@ factor_using_pollard_rho (mpz_t n, int a_int)
   mpz_t a;
   mpz_t g;
   mpz_t t1, t2;
-  int k, l, c, i;
+  int k, l, c;
 
   debug ("[pollard-rho (%d)] ", a_int);
 
@@ -204,6 +204,7 @@ S2:
       mpz_set (x1, x);
       k = l;
       l = 2 * l;
+      unsigned int i;
       for (i = 0; i < k; i++)
         {
           mpz_mul (x, x, x); mpz_add (x, x, a); mpz_mod (x, x, n);