emacs: do not put quoted reply in primary selection

emacs: do not put quoted reply in primary selection

In current emacs (24.3) select-active-regions is set to t by
default. The reply insertion code sets the region to the quoted
message to make it easy to delete (kill-region or C-w). These two
things combine to put the quoted message in the primary selection.

This is not what the user wanted and is a privacy risk (accidental
pasting of the quoted message). We can avoid some of the problems
by let-binding select-active-regions to nil. This fixes if the
primary selection was previously in a non-emacs window but not if
it was in an emacs window. To avoid the problem in the latter case
we deactivate mark.

One key test (which fails under many simpler "fixes") is: open emacs
24.3 with notmuch, open 2 windows (viewing different notmuch buffers),
highlight some text in one, and then reply to a message in the
other. In many of my earlier attempts to fix this big this test fails.