Support a new ANDROID_AAPT_IGNORE env var.

AAPT has a fixed built-in list of files and directories
to ignore when parsing resource files. Over the years we
always had developers requiring specific patterns.
If the env var ANDROID_AAPT_IGNORE is set, it is parsed
to find which file/directory patterns to ignore.
Otherwise a default is used that matches the current behavior.

Added a command-line option for it:
  aapt di --ignore-assets "foo*:*.blah"

SDK Bug: 5343 24067

Change-Id: Ia4caa2a8188c8c1df143f884e459b8182645995f
diff --git a/tools/aapt/AaptAssets.h b/tools/aapt/AaptAssets.h
index d5345b2..52751c7 100644
--- a/tools/aapt/AaptAssets.h
+++ b/tools/aapt/AaptAssets.h
@@ -22,6 +22,10 @@
 
 using namespace android;
 
+
+extern const char * const gDefaultIgnoreAssets;
+extern const char * gUserIgnoreAssets;
+
 bool valid_symbol_name(const String8& str);
 
 class AaptAssets;