gitweb: Silence stderr in parse_commit*() subroutines
git-rev-list command in parse_commit() and parse_commits() can fail
because $commit_id doesn't point to a valid commit; for example if we
are on unborn branch HEAD doesn't point to a valid commit.
In this case git-rev-list prints
fatal: bad revision 'HEAD'
on its standard error. This commit silences this warning, at the cost
of using shell to redirect it to /dev/null, and relying on
quote_command() to protect against code injection.
Note however that such error message from git (from extrenal command)
usually but not always does not appear in web server logs.
Reported-by: rajesh boyapati <boyapatisrajesh@gmail.com>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>