Use ngx_chain_get_free_buf() in pipe input filters.

No functional changes.
Trailing whitespace fix.
Resolver: improved code readability.

Renamed ngx_resolver_query_t to ngx_resolver_hdr_t as it describes
the header that is common to DNS queries and answers.

Replaced the magic number 12 by the size of the header structure.

The other changes are self-explanatory.
Resolver: removed unnecessary casts.
Resolver: fixed response processing.

Stricten response header checks: ensure that reserved bits are zeroes,
and that the opcode is "standard query".

Fixed the "zero-length domain name in DNS response" condition.
Resolver: fixes in A processing.

Verify that class of RR is "IN".
Verify that RR data length is exactly four octets.
Correctly shift to the next RR if RR type is unknown.
Resolver: fixes in PTR processing.

Verify that class of RR is "IN".
Verify that RR data length is non-zero.
Core: externalized ngx_cmp_sockaddr().

It's also extended with the "cmp_port" argument to indicate
whether ports should be compared as well, or only addresses.
Resolver: fixed indentation.
Changed resolver API to use ngx_addr_t.
Resolver: implemented IPv6 address to name resolving.
Resolver: implemented IPv6 name to address resolving.
The "ipv6=" boolean parameter of the "resolver" directive.

When set to "off", only IPv4 addresses will be resolved,
and no AAAA queries are ever sent.
Resolver: lookups are case-insensitive.
nginx-1.5.8-RELEASE
release-1.5.8 tag
Version bump.
SPDY: use predefined constant for size of the Stream-ID field.

No functional changes.
Typo fixed.
Resolver: use minimum TTL for caching (ticket #329).