cond: don't rely on mtime for condition management

TIL, using mtimes for tracking event orderings is a monumentally bad
idea (queue the nodding UNIX-beards). Mtimes are in wallclock time which
is not necessarily monotonically increasing. A user may adjust the time,
an NTP daemon will continously tune the clock and so on.

Instead, store an explicit generation number in each condition file,
which will be monotonically increased by finit on each reconf.

src/cond.h

@@ -15,6 +15,7 @@ typedef enum cond_state {
 
 const char     *condstr      (enum cond_state s);
 const char     *cond_path    (const char *name);
+unsigned int    cond_get_gen (const char *path);
 enum cond_state cond_get_path(const char *path);
 enum cond_state cond_get     (const char *name);
 enum cond_state cond_get_agg (const char *names);
@@ -25,6 +26,7 @@ void cond_set     (const char *name);
 void cond_clear   (const char *name);
 void cond_reload  (void);
 void cond_reassert(const char *pat);
+void cond_init    (void);
 
 #endif	/* FINIT_COND_H_ */