Fix issues that will be present in C++11

- char16_t is a distinct type, so stay consistent
  with it throughout the code base.
- char16_t is defined as minimum size of 16 bits.
  Since we mmap and cast data structures onto raw memory,
  we need a precise definition (uint16_t), so we cast between
  that (and static_assert that they are the same size).

Change-Id: I869c32637543bbcfb39d2643e7d9df10d33acd3c
diff --git a/tools/aapt/AaptXml.cpp b/tools/aapt/AaptXml.cpp
index 708e405..b04a55d 100644
--- a/tools/aapt/AaptXml.cpp
+++ b/tools/aapt/AaptXml.cpp
@@ -41,7 +41,7 @@
     }
 
     size_t len;
-    const uint16_t* str = tree.getAttributeStringValue(attrIndex, &len);
+    const char16_t* str = tree.getAttributeStringValue(attrIndex, &len);
     return str ? String8(str, len) : String8();
 }
 
@@ -103,7 +103,7 @@
     if (tree.getAttributeValue(idx, &value) != NO_ERROR) {
         if (value.dataType == Res_value::TYPE_STRING) {
             size_t len;
-            const uint16_t* str = tree.getAttributeStringValue(idx, &len);
+            const char16_t* str = tree.getAttributeStringValue(idx, &len);
             return str ? String8(str, len) : String8();
         }
         resTable.resolveReference(&value, 0);