ENH: Improve handling of old-style compatibility.

  - Remove CMP_0001 (no slash in target name) and restore
    old CMAKE_BACKWARDS_COMPATIBILITY check for it
  - Replace all checks of CMAKE_BACKWARDS_COMPATIBILITY
    with cmLocalGenerator::NeedBackwardsCompatibility calls
  - Create new CMP_0001 to determine whether or not
    CMAKE_BACKWARDS_COMPATIBILITY is used.
    (old = use, new = ignore)
  - Show CMAKE_BACKWARDS_COMPATIBILITY in cache only when
    CMP_0001 is set to OLD or WARN
  - Update documentation of cmake_policy and cmake_minimum_required
    to indicate their relationship and the 2.4 version boundary
  - When no cmake policy version is set in top level makefile
    implicitly call cmake_policy(VERSION 2.4) which restores
    CMAKE_BACKWARDS_COMPATIBILITY and other 2.4 compatibility
  - Fix tests MakeClean and Preprocess to call
    cmake_policy(VERSION 2.6) because they depend on new policies

1 files changed, 7 insertions, 0 deletions

diff --git a/Source/cmCMakeMinimumRequired.h b/Source/cmCMakeMinimumRequired.h
index d7a1b7e..25e77f3 100644
--- a/Source/cmCMakeMinimumRequired.h
+++ b/Source/cmCMakeMinimumRequired.h
@@ -70,6 +70,13 @@ public:
       "                         [FATAL_ERROR])\n"
       "If the current version of CMake is lower than that required "
       "it will stop processing the project and report an error.\n"
+      "When a version higher than 2.4 is specified the command implicitly "
+      "invokes\n"
+      "  cmake_policy(VERSION major[.minor[.patch]])\n"
+      "which sets the cmake policy version level to the version specified.\n"
+      "When version 2.4 or lower is given the command implicitly invokes\n"
+      "  cmake_policy(VERSION 2.4)\n"
+      "which enables compatibility features for CMake 2.4 and lower.\n"
       "The FATAL_ERROR option is accepted but ignored.  It is left from "
       "CMake versions 2.4 and lower in which failure to meet the minimum "
       "version was a warning by default.";