Minor Win32 improvements (#1648)

* Minor Win32 improvements

There is no win32 support for the Android target. This doesn't change that. It does, however, enable experimental support, via an (unpublished) environment variable, to allow exploration of what is required.

Also, there are some signs of vestigial attempts at supporting Windows. As they haven't been run before, they need a little care:

- Updated references from _winreg to winreg (Built-in module was renamed in Python 3.)
- Corrected download URL to Android NDK for the Windows platform
- Supported sdkmanager installer having a different name (.bat extension) on Windows.

- Also corrected trivial formatting error in Exception text, which applies to all platforms.

* Calculate SDK manager path in two steps for clarity

buildozer/targets/android.py

@@ -2,8 +2,9 @@
 Android target, based on python-for-android project
 '''
 
+import os
 import sys
-if sys.platform == 'win32':
+if sys.platform == 'win32' and not os.getenv("KIVY_WIN32_ANDROID_EXPERIMENTAL"):
     raise NotImplementedError('Windows platform not yet working for Android')
 
 from platform import uname
@@ -20,7 +21,6 @@
 DEFAULT_ANDROID_NDK_VERSION = '17c'
 
 import traceback
-import os
 import io
 import re
 import ast
@@ -244,12 +244,17 @@ def apache_ant_dir(self):
 
     @property
     def sdkmanager_path(self):
+        sdk_manager_name = (
+            'sdkmanager.bat'
+            if platform in ('win32', 'cygwin')
+            else 'sdkmanager'
+        )
         sdkmanager_path = join(
-            self.android_sdk_dir, 'tools', 'bin', 'sdkmanager')
+            self.android_sdk_dir, 'tools', 'bin', sdk_manager_name)
         if not os.path.isfile(sdkmanager_path):
             raise BuildozerException(
                 ('sdkmanager path "{}" does not exist, sdkmanager is not'
-                 'installed'.format(sdkmanager_path)))
+                 ' installed'.format(sdkmanager_path)))
         return sdkmanager_path
 
     @property
@@ -314,14 +319,14 @@ def _p4a_have_aab_support(self):
     def _set_win32_java_home(self):
         if 'JAVA_HOME' in self.buildozer.environ:
             return
-        import _winreg
-        with _winreg.OpenKey(
-                _winreg.HKEY_LOCAL_MACHINE,
+        import winreg
+        with winreg.OpenKey(
+                winreg.HKEY_LOCAL_MACHINE,
                 r"SOFTWARE\JavaSoft\Java Development Kit") as jdk:  # @UndefinedVariable
-            current_version, _type = _winreg.QueryValueEx(
+            current_version, _type = winreg.QueryValueEx(
                 jdk, "CurrentVersion")  # @UndefinedVariable
-            with _winreg.OpenKey(jdk, current_version) as cv:  # @UndefinedVariable
-                java_home, _type = _winreg.QueryValueEx(
+            with winreg.OpenKey(jdk, current_version) as cv:  # @UndefinedVariable
+                java_home, _type = winreg.QueryValueEx(
                     cv, "JavaHome")  # @UndefinedVariable
             self.buildozer.environ['JAVA_HOME'] = java_home
 
@@ -410,7 +415,7 @@ def _install_android_ndk(self):
         if platform in ('win32', 'cygwin'):
             # Checking of 32/64 bits at Windows from: https://stackoverflow.com/a/1405971/798575
             import struct
-            archive = 'android-ndk-r{0}-windows-{1}.zip'
+            archive = 'android-ndk-r{0}-windows.zip'
             is_64 = (8 * struct.calcsize("P") == 64)
         elif is_darwin or is_linux or is_freebsd:
             _platform = 'linux' if (is_linux or is_freebsd) else 'darwin'