Add fixes for CVE-2015-8665, CVE-2015-8683 and other vulnerabilities.

Besides fixing the two CVEs mentioned above, this change also pulls two
other commits from libtiff upstream fixing other out-of-bounds reads that do
not have corresponding CVEs and were reported directly in libtiff's bug
tracker.

PR: 205923
Approved by: portmgr (antoine)
Obtained from: libtiff CVS repository
Security: b65e4914-b3bc-11e5-8255-5453ed2e2b49
Security: bd349f7a-b3b9-11e5-8255-5453ed2e2b49