Without this, Z_RLE could under some circumstances read one byte past
the end of the allocated sliding window. This would normally not be a
problem unless the window is right at the end of an allocated page, or
if a bounds checker is being used.

Also added "-motley" to ZLIB_VERSION in zlib.h, so that versions
in-between 1.2.5.1 and 1.2.5.2 that are pulled down from github
can be identified as such if bugs are reported on them.