Help: Document ctest_start initial checkout command variables

Describe the behavior of the ctest_start() command when the
CTEST_CHECKOUT_COMMAND or CTEST_CVS_CHECKOUT variable is set.
Help: Document ctest dashboard client usage

Extend the ctest(1) manual with a section describing configuration
and usage of CTest as a CDash software quality dashboard client.
Help: Add missing space in policy CMP0020 description
Help: Format cmake_policy command documentation

Add reStructuredText markup manually to improve formatting of the
documentation.  Organize the documentation into subsections.
Help: Reference cmake_minimum_required from cmake_policy docs

Note in a few places of the cmake_policy() command documentation
that the cmake_minimum_required() command can set policies too.

Inspired-by: Peter Kümmel <syntheticpp@gmx.net>
Features: Enable compiler extensions by default.

Compilers enable their extensions by default, and disabling them
implicitly can lead to results which are surprising or non-obvious
to debug.

 http://public.kitware.com/pipermail/cmake-developers/2014-May/010575.html
 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/10214
 https://www.mail-archive.com/cmake-developers@cmake.org/msg10116.html
 (Compiler feature extensions by default, 29 May 2014)
Help: Add code example for INSTALL_INTERFACE to cmake-buildsystem.
Merge topic 'backport-doc-include-dirs-example'

6fbd9a8f Help: Add code example for INSTALL_INTERFACE to cmake-buildsystem.
Merge topic 'policy-doc-updates'

b1f4e620 Help: Reference cmake_minimum_required from cmake_policy docs
69a23cb2 Help: Format cmake_policy command documentation
0c4835a3 Help: Add missing space in policy CMP0020 description
Merge topic 'doc-ctest-settings'

2d57a390 Help: Document ctest dashboard client usage
28f73dff Help: Document ctest_start initial checkout command variables
Merge topic 'feature-extensions-by-default'

60a981ea Features: Enable compiler extensions by default.
Help: Use "^^^^" for subsubsection headers

This is the convention suggested in the Sphinx documentation and is
already used in several other places in the CMake documentation.
Update a few places where we were using other characters.
Help: Add documentation style section headers to cmake-developer.7

Give the style guides titles instead of numbers so we can link to them.
Help: Organize documentation style sections in cmake-developer.7

Now that the style guidelines have section titles instead of numbers,
organize them into more well-defined sections.
Help: Document section header underline hierarchy in cmake-developer.7

Explicitly specify the sequence of underline characters we use in the
CMake documentation.  It is the same sequence as that suggested in the
Sphinx documentation, but we have our own descriptions.
Merge topic 'doc-section-header-convention'

793b64e4 Help: Document section header underline hierarchy in cmake-developer.7
05bd31ab Help: Organize documentation style sections in cmake-developer.7
eaafe756 Help: Add documentation style section headers to cmake-developer.7
4207b3a3 Help: Use "^^^^" for subsubsection headers
FindQt4: Use standard section header underline convention

The FindQt4 module is a CMake Domain object of type "module".
Our convention for domain object document titles is "------"
and domain object document sections is "^^^^^^".  Switch to
these within the FindQt4 documentation.
Merge topic 'FindQt4-doc-section-underlines'

06ab7db3 FindQt4: Use standard section header underline convention