gitweb: Make git_get_refs_list do work of git_get_references

gitweb: Make git_get_refs_list do work of git_get_references

Make git_get_refs_list do also work of git_get_references, to avoid
calling git-peek-remote twice.  Change meaning of git_get_refs_list
meaning: it is now type, and not a full path, e.g. we now use
git_get_refs_list("heads") instead of former
git_get_refs_list("refs/heads").

Modify git_summary to use only one call to git_get_refs_list instead
of one call to git_get_references and two to git_get_refs_list.

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