The environment on Windows is case-insensitive. Some environment functions
(such as unsetenv and make_augmented_environ) have always used case-
sensitive comparisons instead, while others (getenv, putenv, sorting in
spawn*) were case-insensitive.
Prevent potential inconsistencies by using case-insensitive comparison in
lookup_env (used by putenv, unsetenv and make_augmented_environ).
Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Stepan Kasal <kasal@ucw.cz> Signed-off-by: Junio C Hamano <gitster@pobox.com>