gitweb: Use list for of open for running git commands, thorougly.

gitweb: Use list for of open for running git commands, thorougly.

Use list form of open for running git commands and reading their
output through pipe, for example

	open my $fd, "-|", $GIT, "rev-list", "--header", "--parents", $hash

instead of

	open my $fd, "-|", "$GIT rev-list --header --parents $hash"

Single letter options use ' instead of " as quotes, according to style
used in list form of magic "-|" open.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>