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, 1 insertions, 1 deletions

diff --git a/src/pr.c b/src/pr.c
index 7e6b13cc8..3995c37ce 100644
--- a/src/pr.c
+++ b/src/pr.c
@@ -1165,7 +1165,7 @@ main (int argc, char **argv)
         print_files (n_files, file_names);
       else
         {
-          int i;
+          unsigned int i;
           for (i = 0; i < n_files; i++)
             print_files (1, &file_names[i]);
         }