libxml2: update to 2.9.3

libxml2: update to 2.9.3

Contains security fixes and other bug fixes:

CVE-2015-8242 Buffer overead with HTML parser in push mode (Hugh Davenport)
CVE-2015-7500 Fix memory access error due to incorrect entities boundaries (Daniel Veillard)
CVE-2015-7499-2 Detect incoherency on GROW (Daniel Veillard)
CVE-2015-7499-1 Add xmlHaltParser() to stop the parser (Daniel Veillard)
CVE-2015-5312 Another entity expansion issue (David Drysdale)
CVE-2015-7497 Avoid an heap buffer overflow in xmlDictComputeFastQKey (David Drysdale)
CVE-2015-7498 Avoid processing entities after encoding conversion failures (Daniel Veillard)
CVE-2015-8035 Fix XZ compression support loop (Daniel Veillard)
CVE-2015-7942-2 Fix an error in previous Conditional section patch (Daniel Veillard)
CVE-2015-7942 Another variation of overflow in Conditional sections (Daniel Veillard)
CVE-2015-1819 Enforce the reader to run in constant memory (Daniel Veillard)
CVE-2015-7941_2 Cleanup conditional section error handling (Daniel Veillard)
CVE-2015-7941_1 Stop parsing on entities boundaries errors (Daniel Veillard)

Signed-off-by: Marcel Lorenz <marcel.lorenz@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>