Added -Wpointer-arith gcc flag, and fixed the resulting warnings.

diff --git a/configure b/configure
index 36798bc..c2b9fd4 100755
--- a/configure
+++ b/configure
@@ -10668,7 +10668,7 @@
 
 if test "x${GCC}" = "xyes"
 then
-  CFLAGS="$CFLAGS -Wall"
+  CFLAGS="$CFLAGS -Wall -Wpointer-arith"
   echo "$as_me:$LINENO: checking for gcc strength-reduce bug" >&5
 echo $ECHO_N "checking for gcc strength-reduce bug... $ECHO_C" >&6
 if test "${ac_cv_c_gcc_strength_bug+set}" = set; then