NEW IN WAF 1.9
--------------

* General enhancements:
  - Have Clang detected first on many platforms, in particular on FreeBSD #1528
  - Remove Node.cache_sig and Node.sig so that dependencies are on file contents #1580
  - Change cflags in the beginning / cppflags at the end #1505
  - Merge ${FOO}${BAR} flags in commands executed without a shell (no space added)
  - Interpret empty command-line defines as integer values #1704
  - Waf tools are not cached on "waf configure" by default anymore; pass conf.load(.., cache=True)
  - Enable a consistent progress bar output #1641
  - Add ${VAR?X} constructs in script expressions to enable simple conditional outputs
  - Enable 'waf dist' to package arbitrary symlinks in tarballs #1719
  - Enable regexp objects in @extension besides strings for file extensions
  - Match extensions in the order of last definition
  - Task generators are now processed group-by-group, so the next task generators are
    processed when all tasks in a previous group are complete; bld.post_mode=POST_LAZY
    becomes thus the default (playground/dynamic_build/ examples)
  - Process Qt5 files in the way suggested by the Qt documentation
  - Installation methods install_files/install_as/symlink_as create regular task generators
    and regular tasks so that installation outputs can be re-used easily
  - Subclass waflib.Build.ConfiguredContext to enable configuration-dependent user commands

* Performance highlights:
  - Reduce the key size in bld.task_sigs by adding bld.node_sigs and bld.imp_sigs
  - Remove __hash__ and __eq__ from Context, Node and Task #1629
  - Make lazy visual studio detection the default
  - Remove the uses of run_once that can consume a lot of memory; add a proper LRU cache
  - Enable pre-forked builds by default to achieve faster builds, up to 2x speedup on short-lived processes
  - Enable faster consumers in Runner.py
  - Add the tool 'nobuild.py' to help with performance troubleshooting
  - Enable profiling with the --profile command-line option

* API changes:
  - The minimum Python version required is Python 2.5
  - Add Task.get_cwd()
  - Remove the duplicate split() functions from Utils
  - Remove the command called "update"
  - Remove Utils.nogc
  - Remove Configure.err_handler
  - Remove TaskBase.attr() which was never used
  - Remove Build.POST_BOTH which was never used
  - Remove Task.dep_vars as it is never used (define Task.vars on instances if necessary)
  - Remove the unused attribute 'mac_resources', use 'mac_files' instead (see demos/mac_app)
  - Remove qt4 and kde4 from the default modules
  - Refactored msvc.py
  - Task.sig_vars, Task.sig_explit_deps and Task.sig_implicit_deps return None
  - Use relative paths in apply_incpaths by default (and absolute ones when paths cross drives)
  - Modify Utils.run_once so that it accepts a list of *args
  - Better consistency between check_cfg and check_cc variables
  - task_gen.mapping and task_gen.prec are not defined by default on instances anymore, but
    instances can still define their own mappings to override the defaults, but in
    that case all mappings/precedences must be present. These features were not used in Waf 1.8.
  - Do not truncate the _task suffix from Task class names
  - Task.exec_command will use @argfile when command-line limits are exceeded