Merge topic 'doc-ctest_update'

1b18180e Help: Document CTest Git fetch-and-reset behavior
558e4d1e Help: Document ctest_update branch following behavior

Help/command/ctest_update.rst

@@ -25,3 +25,7 @@ The options are:
   have otherwise printed to the console.  CTest will still report
   the new revision of the repository and any conflicting files
   that were found.
+
+The update always follows the version control branch currently checked
+out in the source directory.  See the :ref:`CTest Update Step`
+documentation for more information.

Help/manual/ctest.1.rst

@@ -589,6 +589,11 @@ Configuration settings to specify the version control tool include:
   * `CTest Script`_ variable: :variable:`CTEST_GIT_COMMAND`
   * :module:`CTest` module variable: ``GITCOMMAND``
 
+  The source tree is updated by ``git fetch`` followed by
+  ``git reset --hard`` to the ``FETCH_HEAD``.  The result is the same
+  as ``git pull`` except that any local moficiations are overwritten.
+  Use ``GITUpdateCustom`` to specify a different approach.
+
 ``GITInitSubmodules``
   If set, CTest will update the repository's submodules before updating.