tests: paint skipped tests in blue

Skipped tests indicate incomplete test coverage.  Whilst this is not a
test failure or other error, it's still not a complete success.

Other testsuite related software like automake, autotest and prove
seem to use blue for skipped tests, so let's follow suit.
Signed-off-by: NAdam Spiers <git@adamspiers.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -182,7 +182,7 @@ then
 		error)
 			tput bold; tput setaf 1;; # bold red
 		skip)
-			tput bold; tput setaf 2;; # bold green
+			tput setaf 4;; # blue
 		warn)
 			tput setaf 3;; # brown/yellow
 		pass)