In commit 86f3cd0f (cmMakefile: Require the localGenerator in the
constructor, 2015-04-27) we added use of GetDefinition to the
Initialize method.  Set SuppressWatches before calling this method
since GetDefinition checks it.

Create snapshots for buildsystem directories during configure time.

This class will be extended in follow up commits to snapshot
all values in the cmState.

Move the contents of cmMakeile::SetLocalGenerator to the Initialize
method.

Pass the parent though cmGlobalGenerator::CreateLocalGenerator.

This will make it easy to initialize state scopes independent of
cmMakefile.

There is no need to duplicate these on every cmMakefile.

It is no longer necessary to be able to copy it.  Additionally, this
gives us one less reason to copy cmTarget.

Match the names used in cmake code.

They are maintained as containing the same content as the 'home'
directories, but they are never read from.

Fix some comments and help strings which confused the two by
name. They actually mean what is called CMAKE_SOURCE_DIR in
cmake code.

The version with a null first parameter is now equivalent.

Call the Internal method with equivalent parameters, passing a null first
argument.

A duplicate path computation exists inside the external_in condition now,
but that is harmless at this point.

Because all external callers of this method pass a null first
parameter, this change has no effect for them.

This also makes it obvious that the CMAKE_PARENT_LIST_FILE is set to
the name of the file being read itself for CMakeLists.txt files,
which may not make any sense.

Remove other intermediate variables.

This makes it easier to reason about follow-up commits.

Such files are delegates from other files, and so they set the
CMAKE_PARENT_LIST_FILE to the originator.  They also may set a
policy scope.