Merge pull request apple#4174 from jzhou77/release-6.2

Update release notes and download links.

Merge pull request apple#4000 from xumengpanda/mengxu/ha-code-read

Add comments  to TLog, SS, and DD related code

Merge pull request apple#3897 from xumengpanda/mengxu/62-doc

Update downloads.rst for 6.2.27

Merge pull request apple#3859 from etschannen/release-6.3

Merge Release 6.2 into Release 6.3

Merge pull request apple#3853 from etschannen/release-6.2

Added logging for the ping latencies for all network connections

Merge pull request apple#3836 from etschannen/feature-fix-fault-toler…

…ance

Fixed a number of problems with the fault tolerance calculation when configured with regions

Merge pull request apple#3812 from etschannen/release-6.3

Merge release 6.2 into release 6.3

Merge pull request apple#3799 from etschannen/feature-apiverison-batc…

…h-error

Protect api versions older than 630 from seeing batch_transaction_throttled

Merge pull request apple#3713 from etschannen/release-6.3

fixed a compiler warning

Merge pull request apple#3694 from etschannen/release-6.2

Fixed a pathology where reopening a failed connection could take multiple seconds