tests/basics/lexer: Add line continuation tests for lexer.

Tests for an issue with line continuation failing in paste mode due to the
lexer only checking for \n in the "following" character position, before
next_char() has had a chance to convert \r and \r\n to \n.

tests/basics/lexer.py

@@ -27,6 +27,14 @@ print(eval("1\r"))
 print(eval("12\r"))
 print(eval("123\r"))
 
+# line continuation
+print(eval("'123' \\\r '456'"))
+print(eval("'123' \\\n '456'"))
+print(eval("'123' \\\r\n '456'"))
+print(eval("'123'\\\r'456'"))
+print(eval("'123'\\\n'456'"))
+print(eval("'123'\\\r\n'456'"))
+
 # backslash used to escape a line-break in a string
 print('a\
 b')