Allow specifying the map's initial maxBounds in a different gcs.

[manthey]

If the bounds are known in a gcs other than the interface gcs, they had to be converted first.

This change makes it easier to initialize a map with a stereographic projection, where the unitsPerPixel can be specified to determine the scope of the area shown (since it could be infinite). For example,

var gcs = '+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs'
var unitsPerPixel = 10000
geo.map({
  gcs: gcs, 
  maxBounds: {
    left: -unitsPerPixel * 128, 
    right: unitsPerPixel * 128,
    bottom: -unitsPerPixel * 128,
    top: unitsPerPixel * 128,
    gcs: gcs
  },
   unitsPerPixel: unitsPerPixel
});