docs: add link to notmuch mutttips

Signed-off-by: Karel Zak <kzak@redhat.com>
explicitly call mutt_refresh() prior to endwin() to force a screen redraw.

[4903e80356d3] removed the call, but some environments (screen+xterm under
SuSE11/12) don't properly flush without it prior to the endwin() call
fix potential buffer overflow in off-by-one bounds checking error

closes #3635
increase string size by one byte to accomodate the terminating null character in fscanf() since the maximum field width does not include it

closes #3636

hat tip: Will Fiveash
use of sscanf() had undefined behavior, replace with simple parsing instead

see #3636
use mkdtemp() to create temporary directory rather than mktemp() followed by mkdir()

closes #3637