t8005: convert CP1251 character set to ISO8859-5

t8005: convert CP1251 character set to ISO8859-5

On IRIX 6.5 CP1251 is unknown, but WIN1251 (which seems to be a
non-standard name) is known.  On Solaris 10, the opposite is true.  Solaris
also knows CP1251 as WINDOWS-1251, but this too is not recognized on IRIX.
I could not find a name that both platforms recognized for this character
set.

An alternative character set which covers the same alphabet seems to be the
ISO8859-5 character set.  Both platforms support this character set, so use
it instead.

This allows t8005.4 to pass on Solaris 7, and part of the test to pass on
IRIX. (My IRIX can't convert SJIS to UTF-8 :(

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>