Added ngx_filename_cmp() with "/" sorted to the left.

This patch fixes incorrect handling of auto redirect in configurations
like:

    location /0  { }
    location /a- { }
    location /a/ { proxy_pass ... }

With previously used sorting, this resulted in the following locations
tree (as "-" is less than "/"):

        "/a-"
    "/0"    "/a/"

and a request to "/a" didn't match "/a/" with auto_redirect, as it
didn't traverse relevant tree node during lookup (it tested "/a-",
then "/0", and then falled back to null location).

To preserve locale use for non-ASCII characters on case-insensetive
systems, libc's tolower() used.

src/core/ngx_string.c

diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index d3ff368..fe6b1ee 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -853,6 +853,46 @@
 
 
 ngx_int_t
+ngx_filename_cmp(u_char *s1, u_char *s2, size_t n)
+{
+    ngx_uint_t  c1, c2;
+
+    while (n) {
+        c1 = (ngx_uint_t) *s1++;
+        c2 = (ngx_uint_t) *s2++;
+
+#if (NGX_HAVE_CASELESS_FILESYSTEM)
+        c1 = tolower(c1);
+        c2 = tolower(c2);
+#endif
+
+        if (c1 == c2) {
+
+            if (c1) {
+                n--;
+                continue;
+            }
+
+            return 0;
+        }
+
+        /* we need '/' to be the lowest character */
+
+        if (c1 == 0 || c2 == 0) {
+            return c1 - c2;
+        }
+
+        c1 = (c1 == '/') ? 0 : c1;
+        c2 = (c2 == '/') ? 0 : c2;
+
+        return c1 - c2;
+    }
+
+    return 0;
+}
+
+
+ngx_int_t
 ngx_atoi(u_char *line, size_t n)
 {
     ngx_int_t  value;