Dedicated directory for synchronizable assets.

Check only "sync" directory when synchronizing assets to avoid undesired
coping of other files.

git-svn-id: svn+ssh://svn.code.sf.net/p/cmusphinx/code/trunk/pocketsphinx-android@12447 94700074-3cef-4d97-a70e-9c8c206c02f5