Upgrade to libxml 2.9.2 and libxslt 1.1.28

third_party/libxml/src/README.tests

                        README.tests
 
    Instructions for standalone test regressions of libxml2
 
 libxml2-tests-$version.tar.gz contains 3 standalone C programs as well
 as a large amount of tests and results coming from libxml2 itself and
 from W3C, NIST, Sun Microsystems, Microsoft and James Clark. Each C
 program has a different testing purpose:
 
   runtest.c : runs libxml2 basic internal regression tests
   runsuite.c: runs libxml2 against external regression tests
   testapi.c : exercises the library public entry points
   testchar.c: exercise the check of character ranges and UTF-8 validation
 
 The command:
 
+  make check
+or
   make -f Makefile.tests check
 
 should be sufficient on an Unix system to build and exercise the tests
 for the version of the library installed on the system. Note however
 that there isn't backward compatibility provided so if the installed
-version is older to the testsuite one, failing to compile or run the tests
+version is older than the testsuite one, failing to compile or run the tests
 is likely. In any event this won't work with an installed libxml2 older
 than 2.6.20.
-Building on other platfroms should be a matter of compiling the C files
+
+Building on other platforms should be a matter of compiling the C files
 like any other program using libxml2, running the test should be done
 simply by launching the resulting executables.
 
+Also note the availability of a "make valgrind" target which will run the
+above tests under valgrind to check for memory errors (but this relies
+on the availability of the valgrind command and take far more time to
+complete).
+
 Daniel Veillard
-Thu Jul 24 2008
+Mon May  7 2012
+