Make batches consistent with shell script behavior.

Batch reads from CMake cache, if necessary, when the option is not passed explicitly.

Docs/GettingStarted.dox

@@ -143,8 +143,6 @@ A number of build options can be defined explicitly when invoking the above cmak
 
 Note that build option values specified via command line are cached by CMake. The cached values will be used by CMake in the subsequent invocation. That is, the same build options are not required to be specified again and again. Once a non-default build option value is being cached, it can only be reverted back to its default value by explicitly setting it via command line. That is, simply by NOT passing the corresponding build option would not work. One way to revert all the build options to their default values is by clearing the CMake cache by calling cmake_clean.bat or cmake_clean.sh.
 
-With the exception of these two build options on Windows platform: ENABLE_64BIT and USE_MKLINK. Because they are used as both batch option and build option. On the batch side, unfortunately, they must always be passed to supply a non-default value.
-
 
 \page Running Running Urho3D script host application
 

Readme.txt

@@ -406,11 +406,6 @@ NOT passing the corresponding build option would not work. One way to revert all
 the build options to their default values is by clearing the CMake cache by
 calling cmake_clean.bat or cmake_clean.sh.
 
-With the exception of these two build options on Windows platform: ENABLE_64BIT
-and USE_MKLINK. Because they are used as both batch option and build option. On
-the batch side, unfortunately, they must always be passed to supply a non-
-default value.
-
 
 History
 -------

cmake_android.bat

@@ -25,6 +25,7 @@
 set "build=Source\Android"
 set "source=.."
 set "use_mklink="
+if exist Build\CMakeCache.txt. for /F "eol=/ delims=:= tokens=1-3" %%i in (Build\CMakeCache.txt) do if "%%i" == "USE_MKLINK" set "use_mklink=%%k"
 :loop
 if not "%1" == "" (
     if "%1" == "-DUSE_MKLINK" set "use_mklink=%~2"

cmake_vs2008.bat

@@ -24,9 +24,11 @@
 cmake -E make_directory Build
 set "arch="
 set "version=9 2008"
+if exist Build\CMakeCache.txt. for /F "eol=/ delims=:= tokens=1-3" %%i in (Build\CMakeCache.txt) do if "%%i" == "ENABLE_64BIT" if "%%k" == "1" set "arch= Win64"
 :loop
 if not "%1" == "" (
     if "%1" == "-DENABLE_64BIT" if "%~2" == "1" set "arch= Win64"
+    if "%1" == "-DENABLE_64BIT" if "%~2" == "0" set "arch="
     if "%1" == "VERSION" set "version=%~2"
     shift
     shift