Merge branch 'jc/prune-all'

We used the approxidate() parser for "--expire=<timestamp>" options
of various commands, but it is better to treat --expire=all and
--expire=now a bit more specially than using the current timestamp.
Update "git gc" and "git reflog" with a new parsing function for
expiry dates.

* jc/prune-all:
  prune: introduce OPT_EXPIRY_DATE() and use it
  api-parse-options.txt: document "no-" for non-boolean options
  git-gc.txt, git-reflog.txt: document new expiry options
  date.c: add parse_expiry_date()

date.c

@@ -711,6 +711,28 @@ int parse_date_basic(const char *date, unsigned long *timestamp, int *offset)
 	return 0; /* success */
 }
 
+int parse_expiry_date(const char *date, unsigned long *timestamp)
+{
+	int errors = 0;
+
+	if (!strcmp(date, "never") || !strcmp(date, "false"))
+		*timestamp = 0;
+	else if (!strcmp(date, "all") || !strcmp(date, "now"))
+		/*
+		 * We take over "now" here, which usually translates
+		 * to the current timestamp.  This is because the user
+		 * really means to expire everything she has done in
+		 * the past, and by definition reflogs are the record
+		 * of the past, and there is nothing from the future
+		 * to be kept.
+		 */
+		*timestamp = ULONG_MAX;
+	else
+		*timestamp = approxidate_careful(date, &errors);
+
+	return errors;
+}
+
 int parse_date(const char *date, char *result, int maxlen)
 {
 	unsigned long timestamp;