Fix realpath/toAbsolutePath for stdio/currentString

Not actual files, so don't prepend a directory

Author: d-torrance

M2/Macaulay2/d/actors5.d

@@ -1333,6 +1333,7 @@ setupfun("readlink",readlinkfun);
 
 realpathfun(e:Expr):Expr := (
      when e is f:stringCell do (
+	  if f.v === "stdio" || f.v === "currentString" then return e;
      	  when realpath(expandFileName(f.v))
      	  is null do buildErrorPacket(syscallErrorMessage("realpath"))
      	  is p:string do toExpr(p)

M2/Macaulay2/m2/startup.m2.in

@@ -154,7 +154,12 @@ if firstTime then (
      concatPath = (dir, name) -> if isAbsolutePath name then name else concatenate(
 	 dir, if not match("/$", dir) then "/", name);
 
-     toAbsolutePath = pth -> if pth =!= "stdio" and not isAbsolutePath pth then "/" | relativizeFilename("/", pth) else pth;
+     toAbsolutePath = pth -> (
+	 if (
+	     pth =!= "stdio"         and
+	     pth =!= "currentString" and
+	     not isAbsolutePath pth)
+	 then "/" | relativizeFilename("/", pth) else pth);
 
      use = x -> x;				  -- temporary, until methods.m2