ENH: Added INSTALL(CODE) mode to allow inline specification of install script code.  This reduces the need for configuring an install script that needs some variable settings because the install code can set thing up first.

ENH: More system variables, more operators, more commands, fix some string issues and some cmake arguments issues

ENH: fix re-run of cmake based on configured files that are done with copy if different and never change

ENH: Split CMAKE_STANDARD_LIBRARIES into per-language variables CMAKE_<lang>_STANDARD_LIBRARIES.  This is needed to get programmable language support working with Visual Studio generators.  It makes sense anyway.

ENH: Restored implementation of AddCustomCommandToCreateObject.  Updated it to use newer custom command functionality.

BUG: Install scripts should honor EXCLUDE_FROM_ALL options for subdirectories.  This addresses bug#3100.

ENH: Added support for multiple outputs generated by a single custom command.  For Visual Studio generators the native tool provides support.  For Xcode and Makefile generators a simple trick is used.  The first output is considered primary and has the build rule attached.  Other outputs simply depend on the first output with no build rule.  During cmake_check_build_system CMake detects when a secondary output is missing and removes the primary output to make sure all outputs are regenerated.  This approach always builds the custom command at the right time and only once even during parallel builds.