Move initialization of log_all_ref_updates

Move initialization of log_all_ref_updates

The patches to prevent Porcelainish that require working tree
from doing any damage in a bare repository make a lot of sense,
and I want to make the is_bare_git_dir() function more reliable.

In order to allow the repository owner override the heuristic
implemented in is_bare_git_dir() if/when it misidentifies a
particular repository, it would make sense to introduce a new
configuration variable "[core] bare = true/false", and make
is_bare_git_dir() notice it.

The scripts would do a 'repo-config --bool --get core.bare' and
iff the command fails (i.e. there is no such variable in the
configuration file), it would use the heuristic implemented at
the script level [*1*].

However, setup_git_env() which is called a lot earlier than we
even read from the repository configuration currently makes a
call to is_bare_git_dir(), in order to change the default
setting for log_all_ref_updates.  It somehow feels that this is
a hack.

By the way, [*1*] is another thing I hate about the current
config mechanism.  "git-repo-config --get" does not know what
the possible configuration variables are, let alone what the
default values for them are.  It allows us not to maintain a
centralized configuration table, which makes it easy to
introduce ad-hoc variables and gives a warm fuzzy feeling of
being modular, but my feeling is that it is turning out to be a
rather high price to pay for scripts.

Signed-off-by: Junio C Hamano <junkio@cox.net>