fix construction of file URI by t/external-entities.t

This adjusts the test case to contruct a valid file
URI on MSWin32, fixing test failures observed on Strawberry.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
fix remaining issue with t/external-entities.t on Strawberry

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
MARC::File::XML 1.0.3 release

Signed-off-by: Galen Charlton <gmc@esilibrary.com>