This patch renames remotenames.py to logexchange.py, test-remotenames.t to
test-logexchange.t. Also this patch renames the directory in which the data is
stored from remotenames to logexchange. After this patch, data about bookmarks
and branches from a server we pull is stored in
`.hg/logexchange/(bookmarks|branches)` files.
Thanks to smf for the suggestion.
Differential Revision: https://phab.mercurial-scm.org/D1607
