merge: upstream inotify

 * add feature file monitoring with Linux inotify
 * Change direct mutt_getch() callers to handle new mail event.
 * Add new timeout functions to work with inotify monitors.
 * Quick fix for ncurses buffering issue with inotify polling.
 * Move mutt_getch() timeout value into curs_lib.c
 * Convert context and buffy to use nanosecond timestamps.
 * Work around open mailbox monitor code check issue.
 * Fix MonitorContextDescriptor update on removal.
 * Reset all MonitorContext state on context removal.
 * tidy upstream changes