ENH: Add NSIS compression

Modules/NSIS.template.in

@@ -78,6 +78,9 @@ FunctionEnd
   Name "@CPACK_PACKAGE_INSTALL_DIRECTORY@"
   OutFile "@CPACK_TOPLEVEL_DIRECTORY@/@CPACK_OUTPUT_FILE_NAME@"
 
+  ;Set compression
+  SetCompressor @CPACK_NSIS_COMPRESSOR@
+
 ;--------------------------------
 ;Interface Settings
 

Source/CPack/cmCPackNSISGenerator.cxx

@@ -232,6 +232,7 @@ int cmCPackNSISGenerator::InitializeInternal()
     this->SetOptionIfNotSet("CPACK_NSIS_DELETE_ICONS", 
                             deleteStr.str().c_str());
     }
+  this->SetOptionIfNotSet("CPACK_NSIS_COMPRESSOR", "lzma");
 
   return this->Superclass::InitializeInternal();
 }