upgrade OpenSSL to 1.0.1h to fix multiple security vulnerabilities

Details are at https://www.openssl.org/news/secadv_20140605.txt
fix error on Windows when attempting to remove folders having read-only files
downgrade to libpng-1.5.18 to avoid issues related to the sRGB profile

Some changes in libpng 1.6+ cause it issue warning or even not work
correctly with the original HP/MS sRGB profile. The message you may get
is as follows (originally reported on #1763):

libpng warning: iCCP: Not recognizing known sRGB profile that has been edited

It may result in the profile getting removed, as per
http://sourceforge.net/p/png-mng/mailman/message/32029459/