Support for the MapInfo style zoom layering option

[tamas]

According to the corresponding discussion in the mapserver-dev list the followings will be implemented in the trunk:

• The displayable range of the layer can be specified by using the width of the geo-extent of the map in map units in addition to the current MINSCALEDENOM/MAXSCALEDENOM parameters by adding the MINGEOWIDTH/MAXGEOWIDTH parameters to the layer.

• If both MINSCALEDENOM/MAXSCALEDENOM and MINGEOWIDTH/MAXGEOWIDTH are specified the MINSCALEDENOM/MAXSCALEDENOM setting will take precedence.

• The new keywords will be added to the parser.

• The new keywords will be taken into account during the loadLayer copyLayer and writeLayer operations and in the map legend display.

• MapFile reference and MapScript doc. change according to the new items

[tamas]

Added in trunk r7849 and r7855

[dmorissette]

Reassigned to Jeff for docs

[jmckenna]

• added min/maxgeowidth parameters to the layer object documentation