Rewrite http_parse() completely:

Rewrite http_parse() completely:
1. Make sure the last occurrence of each key is used, even if
it is empty, in which case it resets the value to the default.
2. When there is an HTTP encoding error, skip the affected
key-value pair only, but not all subsequent key-value pairs.
3. Do not modify a string returned from getenv(3).
4. Do not assume the NULL pointer is all null bits.