Use faster constructor of Storage file that only reads headers when converting old ExternalLoads files
Use faster constructor of Storage file that only reads headers when converting old ExternalLoads files

git-svn-id: 9e047e1e624cce0a2485e750063112e834f85522@6308 fc29be9c-2cb0-420d-b520-73dbd18add6e

opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core