Phobos: __FILE__ as template default parameter

[Dicebot via Digitalmars-d]

This important feature and can't be simply removed. For example, 
std.experimental.logger also relies on it. It needs to be fixed 
instead.

Two immediate workarounds that come to mmy mind:

1. Make __FILE__ relative to import path
2. Always emit new symbol to object file if __FILE__ is involved