You might want to review this change as it's my first time.  Be gentle. :-)

This enables even impatient people to run tests that require remote
files such as test_normalization and test_codecmaps_*.

Backported to 2.3.

riscospath.extsep, and use os.extsep throughout.

using a build directory just inside the source directory and saving
just one copy of the test data in the source tree, rather than having
a copy in each build directory.

file directly (instead of sucking it all into a list of lines first).

and only if the test input file doesn't exist.

XXX If NormalizationTest.txt is required to run this test, why isn't it
checked into the project?