(and other lexers too)
This commit rectifies earlier change:
in the lex... even inside quotes, a \ followed by space or tab should
expand to space or tab, and a \ followed by newline should be ignored
(as a line continuation).  compatible with the needs of hoststated
(which has the most strict quoted string requirements), and ifstated
(where one commonly does line continuations in strings).
OK deraadt@, OK millert@