* Bugs 15163 16496 fixed [doc]: getdate() page rewritten

* Bugs 15163 16496 fixed [doc]: getdate() page rewritten

  http://bugzilla.scilab.org/15163
  http://bugzilla.scilab.org/16496
  Rewritten page (PDF): http://bugzilla.scilab.org/attachment.cgi?id=5163

  * FIXED:
    - vectorization of getdate(x) was not documented
    - getdate(x) accept fractional seconds, not only integers. Then
      getdate(x)(10) are fractional seconds, not milliseconds.
    - getdate("s") does NOT take leap seconds into account. Proof added in examples.
    - D = getdate() time referential was not documented.
    - getdate("s"): "UTC (Unix Time Convention)" was puzzling, instead of POSIX.
    - The influence of the computer's time zone on getdate(..) results was unclear.
    - The influence of the computer's DST offset on getdate(..) results was undocumented.
  * Short description explicited and clarified.
  * dateTime format: presentation improved, more compact.
  * Examples added.
  * See also: + calendar, clock, datenum

Change-Id: I8b63a87d462b285086a1bff258888ae6cc6624d5