Change version number to 1.2.8.
Update contrib/minizip/iowin32.c for Windows RT [Vollant].
Do not force Z_CONST for C++.

Forcing Z_CONST resulted in an issue when compiling Firefox.  Now
if someone wants to compile zlib as C++ code (which it isn't), now
they will need to #define Z_CONST themselves.
Update some copyright years.
Clean up contrib/vstudio [Roß].
Correct spelling error in zlib.h.
Fix mixed line endings in contrib/vstudio.
zlib 1.2.8