Add test script for git-stripspace.

Add test script for git-stripspace.

These tests check some features that git-stripspace already has
and those that it should manage well: Removing trailing spaces
from lines, removing blank lines at the beginning and end,
unifying multiple lines between paragraphs, doing the correct
when there is no newline at the last line, etc.

It seems that the implementation needs to save the whole line
in memory to be able to manage correctly long lines with
text and spaces conveniently distribuited on them.

Signed-off-by: Carlos Rica <jasampler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>