Configure: moved NGX_SBIN_PATH variable initialization.

It's now initialized in auto/options like the rest of variables
for system paths.

As a side effect, the currently unused macro NGX_SBIN_PATH now
gets the correct value.

auto/install

diff --git a/auto/install b/auto/install
index 254f9bc..f7f686c 100644
--- a/auto/install
+++ b/auto/install
@@ -20,10 +20,6 @@
     ./*)
     ;;
 
-    .)
-        NGX_SBIN_PATH=$NGX_PREFIX/sbin/nginx
-    ;;
-
     *)
         NGX_SBIN_PATH=$NGX_PREFIX/$NGX_SBIN_PATH
     ;;

auto/options

diff --git a/auto/options b/auto/options
index 6bab052..febbc27 100644
--- a/auto/options
+++ b/auto/options
@@ -525,6 +525,7 @@
 fi
 
 
+NGX_SBIN_PATH=${NGX_SBIN_PATH:-sbin/nginx}
 NGX_CONF_PATH=${NGX_CONF_PATH:-conf/nginx.conf}
 NGX_CONF_PREFIX=`dirname $NGX_CONF_PATH`
 NGX_PID_PATH=${NGX_PID_PATH:-logs/nginx.pid}