Merge branch 'bb/date-iso-strict'

"log --date=iso" uses a slight variant of ISO 8601 format that is
made more human readable.  A new "--date=iso-strict" option gives
datetime output that is more strictly conformant.

* bb/date-iso-strict:
  pretty: provide a strict ISO 8601 date format

cache.h

@@ -1039,6 +1039,7 @@ enum date_mode {
 	DATE_SHORT,
 	DATE_LOCAL,
 	DATE_ISO8601,
+	DATE_ISO8601_STRICT,
 	DATE_RFC2822,
 	DATE_RAW
 };