correct handling of --enable-libusb / --disable-libusb in configure.in

configure.in

@@ -209,36 +209,29 @@ dnl not all options have effect at the moment
 AC_SUBST(libusb_libs)
 AC_SUBST(libusb_cflags)
 
-enable_libusb=yes
 AC_MSG_CHECKING([if libusb support has been enabled]);
 AC_ARG_ENABLE(
   libusb,
   [  --enable-libusb         compile with USB support using libusb.  ],
   [ 
-    if test "$enable_libusb" = "yes"; then
+    if test "$enableval" != "no"; then
-      AC_MSG_RESULT(yes)
+      enable_libusb="yes"
-    else
-      AC_MSG_RESULT(no)
     fi
   ],
-  [ 
+  [ enable_libusb="yes" ]
-    enable_libusb="no";
-    AC_MSG_RESULT(no) 
-  ]
 )
-
+AC_MSG_RESULT($enable_libusb) 
-AC_PATH_PROG(libusb_config,libusb-config, :)
 
 if test "$enable_libusb" = "yes"; then
+  AC_PATH_PROG(libusb_config, libusb-config, :)
+
   AC_ARG_WITH(
     libusb-includes,
     [  --with-libusb-includes=DIR  
                           libusb include files are in DIR
                           (default: found by libusb-config).  ],
     [ 
-    if test "$withval" = "no"; then 
+      if test "$withval" != "no"; then 
-     libusb_build_dir=""; 
-    else
         libusb_includepath="$withval" 
         libusb_cflags="-I$withval" 
       fi
@@ -251,7 +244,7 @@ AC_ARG_WITH(
         for libusb_includepath in /usr/include /usr/local/include \
             /usr/include/libusb /usr/local/include/libusb \
             /usr/include/usb /usr/local/include/usb ; do \
-        if test -f "${ibusb_includepath}/libusb.h"; then
+          if test -f "${libusb_includepath}/libusb.h" ; then
             libusb_cflags="-I$libusb_includepath"
             break
           fi
@@ -277,9 +270,7 @@ AC_ARG_WITH(
                           libusb library files are in DIR
                           (default: found by libusb-config).  ],
     [ 
-    if test "$withval" = "no"; then 
+      if test "$withval" != "no"; then 
-     libusb_build_dir=""; 
-    else
         libusb_libs="-L$withval -lusb" 
       fi
     ],