Make PDoc::OpenInclude() support absolute paths.

This was preventing, for example, Lout's languge addon use of the
"open includes" feature, as it was computing absolute paths that
Pe's code didn't seemed to handle (at least when the files where
not on the same dir as the doc being edited).

Sources/PDoc.cpp

@@ -496,6 +496,17 @@ void PDoc::OpenInclude(const char *incl)
 			return;
 		}
 
+		// Handle absolute paths
+		if (strncmp(incl, "/", 1) == 0)
+		{
+			BPath path(incl);
+			if (e.SetTo(path.Path(), true) == B_OK && e.Exists() && e.IsFile())
+			{
+				FailOSErr(e.GetRef(&doc));
+				found = true;
+			}
+		}
+
 		if (! found && fText->GetCWD())
 		{
 			FailOSErr(d.SetTo(fText->GetCWD()));