cmTarget: Use else/if trees rather than an if tree

Skips lots of unnecessary string comparisons.
cmTarget: Factor out common code
cmTarget: Fast path for regular properties
cmTarget: Sort special property checks

The LINK_LIBRARIES property is by *far* the most popular. Move it to the
top. TYPE is second, but with more generator expression usage, that may
change in the future.
cmTarget: Use static strings for special property names

The function is called enough that the std::string/cstr comparisons are
expensive from the strlen. Cache the strings for faster comparisons.
cmTarget: Don't set properties on custom targets

Properties are not required on custom targets.
cmTarget: Only copy GenEx expansions when necessary
cmTarget: Allow caching of empty genex expansions
cmTarget: use hash_set for sets of strings
cmTarget: help the optimizer a bit
cmTarget: use a hash_map for cmTargets typedef
CMake Nightly Date Stamp
CPack: add generators for .7z and .tar.xz
add liblzma source
make cmliblzma compile in vc6
make cmlibarchive use cmliblzma
buildscripts for cmliblzma