t/.gitattributes: only ignore whitespace errors in test files

Only ignore whitespace errors in t/tNNNN-*.sh and the t/tNNNN
subdirectories.  Other files (like test libraries) should still be
checked.

Also fix a whitespace error in t/test-lib.sh.

Signed-off-by: Lea Wiemann <LeWiemann@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/.gitattributes

@@ -1 +1,2 @@
-* -whitespace
+t[0-9][0-9][0-9][0-9]-*.sh -whitespace
+t[0-9][0-9][0-9][0-9]/* -whitespace

t/test-lib.sh

@@ -168,7 +168,7 @@ trap 'die' exit
 # environment variables to work around this.
 #
 # In particular, quoting isn't enough, as the path may contain the same quote
-# that we're using. 
+# that we're using.
 test_set_editor () {
 	FAKE_EDITOR="$1"
 	export FAKE_EDITOR