Fixes for the android.branch feature

Use getdefault instead of get (duh)
Add commented option to default.spec for documentation

fix: #12

buildozer/default.spec

@@ -62,6 +62,9 @@ requirements = twisted,kivy
 # (str) Android entry point, default is ok for Kivy-based app
 #android.entrypoint = org.renpy.android.PythonActivity
 
+# (str) python-for-android branch to use, if not master, useful to try
+# not yet merged features.
+#android.branch = master
 
 #
 # iOS specific

buildozer/targets/android.py

@@ -277,7 +277,7 @@ class TargetAndroid(Target):
             cmd('git clean -dxf', cwd=pa_dir)
             cmd('git pull origin master', cwd=pa_dir)
 
-            source = self.buildozer.config.get('app', 'android.branch')
+            source = self.buildozer.config.getdefault('app', 'android.branch')
             if source:
                 cmd('git checkout --track -b %s origin/%s' % (source, source),
                     cwd=pa_dir)