FindRuby: Add support for Ruby 2.0 and 2.1

The most significant change since Ruby 1.9 is the changed path of
config.h, from RbConfig::CONFIG['rubyhdrdir'] to
RbConfig::CONFIG['rubyarchhdrdir'].
Help: Add FindRuby-2 topic release notes
Help: Consolidate FindRuby-2 release notes for 3.0.0
Merge branch 'FindRuby-2' into release
add_definitions: Don't document genex support.

This command does not support generator expressions. The documentation
was mistakenly extended to claim it in commit v3.0.0-rc1~60^2~3 (Help: Mark
up the buildsystem commands documentation, 2014-02-03).
CMP0043: Document old and new interfaces for setting directory property.
Merge branch 'add_definitions-no-genex' into release
Merge branch 'CMP0043-dir-prop' into release
Help: Mention in find_package that cmake-gui step is Windows-only (#14781)

Recently used cmake-gui locations are searched only on Windows because
the Windows registry is used to record the values.  This behavior is
historical and may be removed by a policy in the future so rather than
implementing it on other platforms simply document the current behavior.
Merge branch 'doc-find_package-build-paths' into release
cmake: Fix --check-build-system argument count check (#14784)

This internal option requires two arguments, not just one.  Fix the
argument count required to recognize the option.
Merge branch 'fix-check-build-system-crash' into release
Record more policies on targets when created

Policies CMP0027, CMP0038, and CMP0046 have per-target meaning so
record the policy settings on targets as they are created.
Tests: Simplify and document policy scopes in RunCMake.CMP* tests

Drop unnecessary NO_POLICY_SCOPE options.  Document why the remaining
options are necessary.
FindPython{Interp,Libs}: Search for Python 3.4.

Python 3.4.0rnc1 was released on 2014-02-20.
Merge branch 'fix-policy-scopes' into release
Merge branch 'python-3.4' into release