t3900: use ancient iconv names for backward compatibility

Some old iconv implementations do not have many alternate names and/or
do not match character encoding names case insensitively.  These
implementations can not tell that utf-8 and UTF-8 are the same encoding
and fail when trying to do the conversion.  So use the old names, which
modern implementations still support.

The following conversions were performed:

         utf-8 --> UTF-8
    ISO-8859-1 --> ISO8859-1
         EUCJP --> eucJP

Also update t9129 and t9500 which make use of the test files in t/t3900.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index f4210fb..d539619 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -590,7 +590,7 @@
 	 echo "ISO-8859-1" >> file &&
 	 git add file &&
 	 git config i18n.commitencoding ISO-8859-1 &&
-	 git commit -F "$TEST_DIRECTORY"/t3900/ISO-8859-1.txt &&
+	 git commit -F "$TEST_DIRECTORY"/t3900/ISO8859-1.txt &&
 	 git config --unset i18n.commitencoding &&
 	 gitweb_run "p=.git;a=commit"'
 test_debug 'cat gitweb.log'