When used with lighttpd or mongoose, git-instaweb previously passed a
hard-coded, default value of PATH to the gitweb CGI script. Use the invoking
user's value for PATH for this instead. (This is already implicitly the
behaviour for other web servers supported by git-instaweb.)
Signed-off-by: Chris Webb <chris@arachsys.com> Acked-by: Eric Wong <normalperson@yhbt.net>