CPackRPM: Add component based packaging description and summary

Enable per-component description and summary setting through
CPACK_RPM_<component>_PACKAGE_DESCRIPTION,
CPACK_COMPONENT_<compName>_DESCRIPTION and
CPACK_RPM_<component>_PACKAGE_SUMMARY variables.

Extend the CPackComponentsForAll test to cover these.
Utilities/Release: Update default binary distribution dir to v3.1
BundleUtilities: Ensure framework symlinks and Info.plist exist

This restores Qt SDK 4.8 and OS X >= 10.6.5 codesign compatibility
improving embedding frameworks using correct bundle layout described at:

https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/FrameworkAnatomy.html

1. If Versions/VERSION/Resources/Info.plist is missing, well known
   incorrect locations are checked for Info.plist and Info.plist is
   copied from there, otherwise codesign will fail.

2. Root framework symlinks to binary and Resources are restored to
   point inside Versions/Current, otherwise Qt 4.8 looking for
   Resources/ in framework root will fail.
Help: Document CMAKE_XCODE_ATTRIBUTE_<an-attribute> variable (#15215)
FindCUDA: Remove rpath logic outdated by CMake's own @rpath support

Otherwise binaries end up with two copies of the same value and the OS X
install_name_tool may corrupt them.
FindHg: Do not use cygwin hg on Windows

The cygwin hg client is a text file with a '#!/bin/python" line.
This cannot run on Windows.
Tests/ExternalProject: Skip Windows hg tests with cygwin hg

The cygwin hg client is a text file with a '#!/bin/python" line.
This cannot run on Windows.
Merge topic 'cpack-rpm-component-descriptions'

603ef7fd CPackRPM: Add component based packaging description and summary
Merge topic 'release-upload-version'

c8616203 Utilities/Release: Update default binary distribution dir to v3.1
Merge topic 'fix-OSX-bundle-rpaths-and-Qt5'

41564ff2 BundleUtilities: Ensure framework symlinks and Info.plist exist
Merge topic 'cuda-rpath-osx'

59814cb4 FindCUDA: Remove rpath logic outdated by CMake's own @rpath support
Merge topic 'ExternalProject-no-cygwin-hg-on-windows'

ad984b60 Tests/ExternalProject: Skip Windows hg tests with cygwin hg
Merge topic 'FindHg-no-cygwin-hg-on-windows'

ed997de4 FindHg: Do not use cygwin hg on Windows
Merge topic 'doc-CMAKE_XCODE_ATTRIBUTE'

0ff69dd4 Help: Document CMAKE_XCODE_ATTRIBUTE_<an-attribute> variable (#15215)