Don't set global value buffer-local-vars to anything.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Add weechat-buffer-last-msg and weechat-buffer-last-highlight.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Store buffer modification time in hash.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Add `weechat-buffer-last-{msg,highlight}'.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Add `weechat-reset-buffer-modified'.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Reset modification dates when buffer is visible.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Reset buffer modification date when switching to buffers.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Clarify use of `weechat-last-{message,highlight}-date'.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>