[QGIS-Developer] Compatibility between 2.99 project files and 2.18

[Patrick Dunford]

As of the moment I'm finding that 2.18 has difficulty correctly 
detecting the CRS from a project file saved from the latest master. 
Generally EPSG:3857 is detected as EPSG:4326

Given the master is still a development version is this considered a bug 
in 2.18 or is there still a process of defining the 3.0 project file 
format to the point where it is reasonably compatible with older versions.