core: simplify custom strtod() interface

The strtod_flags() function allowed for fine control of how to
parse strings. However, only two different modes were actually
used: ascii mode ("C" locale) and permissive mode (accept ","
and "." as decimal separator).

The former had already its own function name (ascii_strtod).
Make the latter a separatge function as well (permissive_strtod)
and remove all the flags rigmarole.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/parse-xml.cpp

@@ -168,7 +168,7 @@ static enum number_type parse_float(const char *buffer, double &res, const char
 				first_time = false;
 			}
 			/* Try again in permissive mode*/
-			val = strtod_flags(buffer, &endp, 0);
+			val = permissive_strtod(buffer, &endp);
 		}
 	}