[PATCH] Fix zlib check on RHEL5

I attached here a very small patch to fix the zlib check on RedHat 
Enterprise Linux 5. For some reason zlib.h does not define 
ZLIB_VER_MAJOR and ZLIB_VER_MINOR.


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Davíð Steinn Geirsson
Basis ehf.
user-c892c763c49a@xymon.invalid / (+XXX) XXX-XXXX