Fix display of repeated POST vars

[dairiki]

The keys for POST vars with duplicate names were being (correctly) listed in their orignal order, however all values for each of these keys were (incorrectly) listed for each occurance of the duplicated keys.

This is particularly confusing, e.g., when looking at, e.g. peppercorn-encoded data. By way of example, currently peppercorn data consisting of two simple mappings is currently (incorrectly) displayed as:

Variable	Value
start	u'A:mapping', u'B:mapping'
score	u'1', u'2'
end	u'A:mapping', u'B:mapping'
start	u'A:mapping', u'B:mapping'
score	u'1', u'2'
end	u'A:mapping', u'B:mapping'

With this patch, the same data is correctly displayed as:

Variable	Value
start	u'A:mapping'
score	u'1'
end	u'A:mapping'
start	u'B:mapping'
score	u'2'
end	u'B:mapping'

[mmerickel]

This looks good, thanks!