hgweb: use generator to count parity of horizontal stripes for easier reading. - use web.stripes in all places and consistently - start with parity0 for lists generated in reverse (e.g. changelog)

     1

# should print nothing

     2

# should print ? b/x

     3

? b/x

     4

# should print A b/x

     5

A b/x

     6

# should forget b/x

     7

forgetting b/x

     8

# should print nothing