Add LOCAL_APK_LIBRARIES argument.

This allows you to build apks that link against other
apks using the framework's new shared library apk feature.

Also if you are using LOCAL_APK_LIBRARIES, then LOCAL_DEX_PREOPT
will not be allowed.  This is because using preopt means the
apk is stripped of its dex file, so the pre-installed apk can't
be redexed if its associated library changes.  (Even if the build
system didn't strip the dex, Dalvik still has issues because it
assumes a pre-odex file is always valid.)

Change-Id: I952c0d24f8975f75aff67f78b5faeec91144c3e7
diff --git a/core/package.mk b/core/package.mk
index 3a8e43a..25af8da 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -151,6 +151,7 @@
 LOCAL_DEX_PREOPT :=
 else
 ifeq (,$(TARGET_BUILD_APPS))
+ifeq (,$(LOCAL_APK_LIBRARIES))
 ifneq (,$(LOCAL_SRC_FILES))
 ifndef LOCAL_DEX_PREOPT
 LOCAL_DEX_PREOPT := true
@@ -158,6 +159,7 @@
 endif
 endif
 endif
+endif
 ifeq (false,$(LOCAL_DEX_PREOPT))
 LOCAL_DEX_PREOPT :=
 endif