report: add support for time (basic)

This patch adds support for time values used in reporting fields.
The raw values are always stored as number of seconds since epoch.

The support that comes with this patch is the basic one which allows
only for recognition of strictly formatted date and time in selection
criteria (the format follows a subset of formats defined by ISO 8601):

  date time timezone

  date:
    YYYY-MM-DD (or shortly YYYYMMDD)
    YYYY-MM (shortly YYYYMM), auto DD=1
    YYYY, auto MM=01 and DD=01

  time:
    hh:mm:ss (or shortly hhmmss)
    hh:mm (or shortly hhmm), auto ss=0
    hh (or shortly hh), auto mm=0, auto ss=0

  timezone (always with + or - sign):
    +hh:mm or -hh:mm (or shortly +hhmm or -hhmm)
    +hh or -hh

Or directly the time (number of seconds) since Epoch (1970-01-01 00:00:00 UTC)
when the number value is prefixed by "@":

   @number_of_seconds_since_epoch

This patch also adds aliases for comparison operators
used together with time values which are more intuitive
to use:
  since (as alias for >=)
  after (as alias for >)
  until (as alias for <=)
  before (as alias for <)

For example:

$ lvmconfig --type full report/time_format
time_format="%Y-%m-%d %T %z %Z [%s]"

$ lvs -o name,time vg
  LV    Time
  lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
  lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
  lvol2 2015-04-26 14:52:20 +0200 CEST [1430052740]
  lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]

$ lvs vg -o name,time -S 'time since "2015-04-26 15:00" && time until "2015-06-30"'
  LV    Time
  lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
  lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
  lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]

$ lvs vg -o name,time -S 'time since "2015-04-26 15:00" && time until "2015-06-30 6:00"'
  LV    Time
  lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
  lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]

$ lvs vg -o name,time -S 'time since @1435519541'
  LV    Time
  lvol0 2015-06-28 21:25:41 +0200 CEST [1435519541]
  lvol1 2015-06-30 03:25:43 +0200 CEST [1435627543]
  lvol3 2015-06-30 14:52:23 +0200 CEST [1435668743]

This is basic time recognition support that is directly a part of
libdevmapper. Recognition of more free-form expressions will be a
part of subsequent patches.

lib/properties/prop_common.h

@@ -127,8 +127,9 @@ static int _ ## NAME ## _get (const void *obj, struct lvm_property_type *prop) \
 #define BIN 3
 #define SIZ 4
 #define PCT 5
-#define STR_LIST 6
+#define TIM 6
 #define SNUM 7              /* Signed Number */
+#define STR_LIST 8
 
 #define FIELD_MODIFIABLE 0x00000001
 #define FIELD(type, strct, field_type, head, field, width, fn, id, desc, settable) \