Merge branch 'mc-1.15.x' into mc-1.16.x

src/main/resources/data/computercraft/lua/bios.lua

@@ -681,6 +681,7 @@ if http then
     local nativeCheckURL = http.checkURL
     http.checkURLAsync = nativeCheckURL
     http.checkURL = function(_url)
+        expect(1, _url, "string")
         local ok, err = nativeCheckURL(_url)
         if not ok then return ok, err end
 

src/main/resources/data/computercraft/lua/rom/motd.txt

@@ -21,3 +21,4 @@ The "equip" programs let you add upgrades to a turtle without crafting.
 You can change the color of a disk by crafting or right clicking it with dye.
 You can print on a printed page again to get multiple colors.
 Holding the Ctrl and T keys terminates the running program.
+You can drag and drop files onto an open computer to upload them.