This patch fixes a couple of bugs introduced in CL 210778 and CL 207606:
- apply the same version selection scheme in loader.CreateExtSym that
we're currently using for loader.Create (since the two functions
will be used in the same way by the host object loader)\ 1
- add code to the loader's NewLoader function to create initial map
values for some of the map-based symbol attributes (somewhere along
the line the code to do this seems to have gotten lost, so this
patch adds it back).
- fix a coding error in growAttrBitmaps (wrong bitmap passed to
append when extending attrOnList)