CMake: build expat, apr, apru, zlib, iconv, openssl, httpd, jk and mod_cluster

This is a long-term pet project dedicated to translating Autotools to CMake. The first two target platforms are Windows and Fedora, x86_64. Various flavours of Solaris, HP-UX, FreeBSD and Mac will follow.
I'll use this JIRA for tracking notes and progress. It is noteworthy that the current upstream expat, apr and httpd use CMake to generate MSVC projects, so translating those to generating Linux make files shouldn't be that nightmareish. One Autotools directive at a time...