doc: make i18n man and html
Allow overwrite LANGUAGE and LC_ALL make variables, for make i18n man and html.
After this patch, we can make i18n man and html by following command:
$ make clean all LANGUAGE=ja
# invalid filenames
test-add.t
test-init.t
test-clone.t
test-contrib.t
test-hgweb-raw.t
test-walk.t
# no sockets or fifos
test-hup.t
test-inotify-debuginotify.t
test-inotify-dirty-dirstate.t
test-inotify-issue1208.t
test-inotify-issue1371.t
test-inotify-issue1542.t
test-inotify-lookup.t
test-inotify.t
test-inotify-issue1556.t
# no hardlinks
test-hardlinks.t
test-relink.t
# exec bit problems
test-convert-bzr-114.t
test-convert-bzr-directories.t
test-convert-bzr-merges.t
test-convert-bzr-treeroot.t
test-convert-darcs.t
test-merge-tools.t
# debugstate exec bit false positives
test-dirstate.t
test-filebranch.t
test-merge-remove.t