Added MongoDate::__set_state()

Fixes PHP-904
https://jira.mongodb.org/browse/PHP-904

Allows MongoDate objects exported via var_export() to be parsed.
var_export() is handy when creating test fixtures.
Merged pull request #732
PHP-1219: No more 5.2 in travis or package.
Removed skipifs for PHP 5.3 checks.
Remove pre-PHP 5.3 related macros.
Merged pull request #734
PHP-1218: Added MongoDate::toDateTime() to convert a MongoDate object to PHP's DateTime object.
Extract duplicated code into a helper function.
Merged pull request #733
Move test version requirement to SKIPIF block

See: d363298bf20325c5b22f2e01cf1116efe2cf78f7
Merge pull request #736
Merge branch 'v1.5'
PHP-1220: Ensure topology discovery pings all known hosts

Previously, mongo_discovery_topology would append hosts to the servers array only after creating a new connection. This meant that hosts might get duplicate entries in the list after a failover reconnection (if they were also in the seed list). More significantly, this meant that hosts not in the seed list would be ignored if they already had a persistent connection from a previous request.

After collecting known hosts from an isMaster response, add the host to the servers array if an equivalent definition entry does not exist. This ensures hosts are not ignored, but also avoids adding a duplicate entry for reconnections, which means we will not immediately send isMaster to those hosts in a subsequent next loop iteration (this is OK, as they will be queried during the next isMaster interval).

Additionally, by not adding duplicate entries, we should avoid overflowing the servers array (until replica set size limits are raised), which is currently fixed size.
Increase write concern to avoid random test failures
Merge pull request #735
Merge branch 'v1.5'
BUMP 1.5.6
Back to dev
Merge branch 'v1.5'
PHP on Windows does tricky things with inline, which we can't use in mcon.