Allow get-prebuilts to work from any CWD

The unzip command in get-prebuilts assumed that the CWD
as ./vendor/cm.  This changes allows it to work from any
CWD so now you can do

  ./vendor/cm/get-prebuilts

instead of

  cd ./vendor/cm && ./get-prebuilts

Change-Id: I705191fd84c3ffda6b2e81b7ea7518327cce8081

get-prebuilts

@@ -1,9 +1,12 @@
-mkdir -p `dirname $0`/proprietary
+
+BASEDIR=`dirname $0`
+
+mkdir -p $BASEDIR/proprietary
 
 # Get ROM Manager
-curl -L -o `dirname $0`/proprietary/RomManager.apk -O -L http://download.clockworkmod.com/recoveries/RomManager.apk
+curl -L -o $BASEDIR/proprietary/RomManager.apk -O -L http://download.clockworkmod.com/recoveries/RomManager.apk
 
 # Get Android Terminal Emulator (we use a prebuilt so it can update from the Market)
-curl -L -o `dirname $0`/proprietary/Term.apk -O -L https://github.com/downloads/jackpal/Android-Terminal-Emulator/Term.apk
-unzip -o -d proprietary proprietary/Term.apk lib/armeabi/libjackpal-androidterm3.so
+curl -L -o $BASEDIR/proprietary/Term.apk -O -L https://github.com/downloads/jackpal/Android-Terminal-Emulator/Term.apk
+unzip -o -d $BASEDIR/proprietary $BASEDIR/proprietary/Term.apk lib/armeabi/libjackpal-androidterm3.so