ITS#7964 avoid double-unescaping rewrite rules

ITS#7964 avoid double-unescaping rewrite rules

config_fp_parse_line processes backslash escapes. When existing rewrite
rules were reloaded while inserting a new rule, this caused backslashes
to be lost from every rule except the most recently inserted one.
config_parse_ldif performs similar splitting, but leaves backslashes
alone.