[WMS TIME] Add suuport for multiple interval extents

[assefa]

Dicsussion fro the mailing list :

 From the specs (wms 1.1 annex c c.3), the extent could be defined in 4 ways :
   1) value : A single value.  This is not directly supported in Mapserver but 
there is an easy workwound by specifying the same value as min and max

   2) value1,value2,value3,... a A list of multiple values. This is not 
supported in Mapserver.

   3) min/max/resolution An interval defined by its lower and upper
      bounds and its resolution.  This is supported in Mapserver (Note that 
the resolution is not supported)

   4) min1/max1/res1,min2/max2/res2,... a A list of multiple intervals. Not 
supported


 The idea here is to initally support item4.

[assefa]

I have added the support of Item 2 and 4. I have done some initila tests.

 Norm, you can contact me to add additional tests to you set of tests.

 Waiting for addition tests (from Norm and the list) before closing the bug.

[assefa]

Tests added. Transferring to to Jeff for doc update.

[assefa]

change target to 4.8

[assefa]

Reassign to jeff :)

[jmckenna@…]

added extents explanation to doc
(http://mapserver.gis.umn.edu/docs/howto/wms_time_support/)