http.c: don't use curl_easy_strerror prior to curl-7.12.0
http.c: don't use curl_easy_strerror prior to curl-7.12.0

Reverts be22d92 (http: avoid empty error messages for some curl
errors, 2011-09-05) on platforms with older versions of libcURL
where the function is not available.

Signed-off-by: Joachim Schmitz <13de8889aecf8f48d9c799a1f3fb520fa748372a@schmitz-digital.de>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git