fix configure

configure.ac

@@ -253,7 +253,14 @@ AC_ARG_ENABLE(lsr,
 	enable_lsr=yes)
 
 
-AC_ARG_WITH(tremor,[[  --with-tremor[=PFX]         Use Tremor(vorbisidec) integer Ogg-Vorbis decoder (with optional prefix)]], use_tremor=yes; test x$withval != xyes && tremor_prefix="$withval",)
+AC_ARG_WITH(tremor,[[  --with-tremor[=PFX]         Use Tremor(vorbisidec) integer Ogg-Vorbis decoder (with optional prefix)]],
+  if test "x$withval" = xyes -o "x$withval" = xno; then
+    use_tremor="$withval"
+  else
+    use_tremor=yes
+    tremor_prefix="$withval"
+  fi
+,)
 AC_ARG_WITH(tremor-libraries,[  --with-tremor-libraries=DIR Directory where Tremor library is installed (optional)], tremor_libraries="$withval", tremor_libraries="")
 AC_ARG_WITH(tremor-includes,[  --with-tremor-includes=DIR  Directory where Tremor header files are installed (optional)], tremor_includes="$withval", tremor_includes="")