Drop compatibility with CMake < 2.4

Drop all behavior activated by setting CMAKE_BACKWARDS_COMPATIBILITY to
a value lower than 2.4, and generate an error when projects or the user
attempt to do so.  In the error suggest using a CMake 2.8.x release.

Teach cmake_minimum_required to warn about projects that do not require
at least CMake 2.4.  They are not supported by CMake >= 3.0.

Replace the documentation of CMAKE_BACKWARDS_COMPATIBILITY with a
reference to policy CMP0001.

1 files changed, 6 insertions, 11 deletions

diff --git a/Source/cmAddCustomTargetCommand.cxx b/Source/cmAddCustomTargetCommand.cxx
index 4eba886..2a683a4 100644
--- a/Source/cmAddCustomTargetCommand.cxx
+++ b/Source/cmAddCustomTargetCommand.cxx
@@ -25,17 +25,12 @@ bool cmAddCustomTargetCommand
   // Check the target name.
   if(args[0].find_first_of("/\\") != args[0].npos)
     {
-    if(!this->Makefile->NeedBackwardsCompatibility(2,2))
-      {
-      cmOStringStream e;
-      e << "called with invalid target name \"" << args[0]
-        << "\".  Target names may not contain a slash.  "
-        << "Use ADD_CUSTOM_COMMAND to generate files.  "
-        << "Set CMAKE_BACKWARDS_COMPATIBILITY to 2.2 "
-        << "or lower to skip this check.";
-      this->SetError(e.str().c_str());
-      return false;
-      }
+    cmOStringStream e;
+    e << "called with invalid target name \"" << args[0]
+      << "\".  Target names may not contain a slash.  "
+      << "Use ADD_CUSTOM_COMMAND to generate files.";
+    this->SetError(e.str().c_str());
+    return false;
     }
 
   // Accumulate one command line at a time.