fix problems with external module handling. found by benoit boissinot. first fix is to not store module objects in commands.external dict, instead use module names for key into sys.modules. this prevents circular reference during cleanup of aborted transaction. second is to get name right during import of external module.

adding a
adding b
adding t.h
adding t/x
a
NONEXISTENT: No such file or directory
a
b
t.h
t/x
a: No such file or directory
NONEXISTENT: No such file or directory
b
t.h
t/x
a
NONEXISTENT: No such file in rev ce18e5bc5cd3
a
t/x
b
t.h
% -I/-X with relative path should work
b
t.h
t/x
t/x
t/x