ident: trim whitespace from default name/email

ident: trim whitespace from default name/email

Usually these values get fed to fmt_ident, which will trim
any cruft anyway, but there are a few code paths which use
them directly. Let's clean them up for the benefit of those
callers. Furthermore, fmt_ident will look at the pre-trimmed
value and decide whether to invoke ERROR_ON_NO_NAME; this
check can be fooled by a name consisting only of spaces.

Note that we only bother to clean up when we are pulling the
information from gecos or from system files. Any other value
comes from a config file, where we will have cleaned up
accidental whitespace already.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>