make check for custom CRS smarterer

[jgravois]

resolves #1019

took a look at this today and realized that the problem @theashyster reported also causes an unnecessary console error outside of webpack when a simple WGS84 tile service is added to a map.

var map = L.map('map',{crs: L.CRS.EPSG4326}).setView([45,-125], 3);

L.esri.tiledMapLayer({
  url: 'http://services.arcgisonline.com/arcgis/rest/services/ESRI_Imagery_World_2D/MapServer'
}).addTo(map);

instead of checking to see whether a) the map and tiled service are both web mercator and b) if proj4 is available we can instrospect the CRS defined for the map and make sure the supplied code is the same one the service is using.

[theashyster]

Hey, today I found the time to test out the newest version of esri-leaflet and sadly it did not work out as I hoped for.
Before the changes things related to proj4 would go into the else block and show a warning if proj4 was missing (which caused the original issue I described here #1019).
After the changes things related to proj4 goes into the main block and fires lodmap event.
Because of this, I only get the initial map loaded and when I do zooming or dragging around the map no other base map tiles are loaded or even requested to be loaded.

Here is the issue visible on Plunker https://plnkr.co/edit/kFneHCA8CBMpAbg12mwp?p=preview
And if you just change the version to [email protected] in the index.html you would see that it works fine.

[jgravois]

ugh. totally my fault. fix is in #1051.

[theashyster]

Heh, no problem, thanks for the fast fix 👍