Waf 1.9
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* Do not cache waf tool detection
* Fix the vala detection
* Better consistency between check_cfg and check_cc variables
* Let more context commands depend on the configuration
* Rework qt5
* Use relative paths in apply_incpaths (and absolute ones when paths cross drives)
* Provide a more efficient ConfigSet implementation
* Ensure _cache.py are valid python files

and all other issues listed on https://github.com/waf-project/waf/issues

Done
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* Remove the split functions from Utils
* Remove the command called "update"
* Include the tool 'nobuild' by default
* Remove qt4 and kde4 from the default modules
* Detect Clang first on many platforms, in particular on FreeBSD #1528
* Let run_once accept a list of *args
* Remove Node.cache_sig and Node.sig #1580
* Remove __hash__ and __eq__ from Node and Task #1629
* Set cflags in the beginning / cppflags at the end #1505
* Reduce the key size in bld.task_sigs by adding bld.node_sigs and bld.imp_sigs
* Make lazy visual studio detection the default