Fix IPAddress operator==

Summary: IPAddress operator== throws an exception when comparing ip v6 mapped address with unitialized (default constructed) address. With this diff it returns false.

Test Plan: folly unit tests

Reviewed By: bmatheny@fb.com

FB internal diff: D1421280
Allow undefined LZ4_MAX_INPUT_SIZE

Summary:
Because the version of lz4 that ships by default with Ubuntu 13.10 doesn't
define it (but has lz4_decompress_safe, so it's usable)

Test Plan: built on Ubuntu 13.10

Reviewed By: meyering@fb.com

Subscribers: jhj, lesha, kma

FB internal diff: D1433864

@override-unit-failures
Update folly/thrift README with tested deps for Ubuntu 13.10 and 14.04

Test Plan: no

Reviewed By: lesha@fb.com

Subscribers: alandau, jhj, kma

FB internal diff: D1434163