ENH: Updated exporting and importing of targets to support libraries and configurations.

- Created cmExportFileGenerator hierarchy to implement export file generation
  - Installed exports use per-config import files loaded by a central one.
  - Include soname of shared libraries in import information
  - Renamed PREFIX to NAMESPACE in INSTALL(EXPORT) and EXPORT() commands
  - Move addition of CMAKE_INSTALL_PREFIX to destinations to install generators
  - Import files compute the installation prefix relative to their location when loaded
  - Add mapping of importer configurations to importee configurations
  - Rename IMPORT targets to IMPORTED targets to distinguish from windows import libraries
  - Scope IMPORTED targets within directories to isolate them
  - Place all properties created by import files in the IMPORTED namespace
  - Document INSTALL(EXPORT) and EXPORT() commands.
  - Document IMPORTED signature of add_executable and add_library
  - Enable finding of imported targets in cmComputeLinkDepends

Source/cmIncludeExternalMSProjectCommand.cxx

@@ -51,8 +51,7 @@ bool cmIncludeExternalMSProjectCommand
 
     // Create a target instance for this utility.
     cmTarget* target=this->Makefile->AddNewTarget(cmTarget::UTILITY, 
-                                                  utility_name.c_str(), 
-                                                  false);
+                                                  utility_name.c_str());
     target->SetProperty("EXCLUDE_FROM_ALL","FALSE");
     std::vector<std::string> no_outputs;
     cmCustomCommandLines commandLines;