Update expat to 2.0.1.

We had one local patch relative to 2.0.0, in "xmltok_impl.c". That
fix isn't in 2.0.1, but an equivalent patch is in expat CVS. I've gone
with the upstream change, and surrounded it with BEGIN/END android-changed
comments.

Bug: 2086506
diff --git a/README b/README
index 585bcc1..fda282a 100644
--- a/README
+++ b/README
@@ -1,5 +1,5 @@
 
-                        Expat, Release 2.0.0
+                        Expat, Release 2.0.1
 
 This is Expat, a C library for parsing XML, written by James Clark.
 Expat is a stream-oriented XML parser.  This means that you register
@@ -25,8 +25,8 @@
 If you are building Expat from a check-out from the CVS repository,
 you need to run a script that generates the configure script using the
 GNU autoconf and libtool tools.  To do this, you need to have
-autoconf 2.52 or newer and libtool 1.4 or newer.  Run the script like
-this:
+autoconf 2.52 or newer and libtool 1.4 or newer (1.5 or newer preferred).
+Run the script like this:
 
         ./buildconf.sh
 
@@ -53,6 +53,10 @@
 line and column numbers and the over-all byte index:
 
         ./configure CPPFLAGS=-DXML_LARGE_SIZE
+        
+However, such a modification would be a breaking change to the ABI
+and is therefore not recommended for general use - e.g. as part of
+a Linux distribution - but rather for builds with special requirements.
 
 After running the configure script, the "make" command will build
 things and "make install" will install things into their proper
@@ -62,7 +66,7 @@
 
 If you are interested in building Expat to provide document
 information in UTF-16 rather than the default UTF-8, follow these
-instructions:
+instructions (after having run "make distclean"):
 
         1. For UTF-16 output as unsigned short (and version/error
            strings as char), run:
@@ -86,8 +90,23 @@
            (Note the additional "w" in the library name.)
 
         3. Run "make buildlib" (which builds the library only).
+           Or, to save step 2, run "make buildlib LIBRARY=libexpatw.la".
 
         4. Run "make installlib" (which installs the library only).
+           Or, if step 2 was omitted, run "make installlib LIBRARY=libexpatw.la".
+           
+Using DESTDIR or INSTALL_ROOT is enabled, with INSTALL_ROOT being the default
+value for DESTDIR, and the rest of the make file using only DESTDIR.
+It works as follows:
+   $ make install DESTDIR=/path/to/image
+overrides the in-makefile set DESTDIR, while both
+   $ INSTALL_ROOT=/path/to/image make install
+   $ make install INSTALL_ROOT=/path/to/image
+use DESTDIR=$(INSTALL_ROOT), even if DESTDIR eventually is defined in the
+environment, because variable-setting priority is
+1) commandline
+2) in-makefile
+3) environment           
 
 Note for Solaris users:  The "ar" command is usually located in
 "/usr/ccs/bin", which is not in the default PATH.  You will need to