set SO_KEEPALIVE on all connections

The MySQL client libraries do this automatically, so it makes sense to
do so here, as well.
Remove unjustified uses of bare 'except' clause
Parse full 4-byte unsigned int for server_thread_id.
handle connection errors properly (fixes petehunt/PyMySQL/#89)
use SOL_SOCKET instead of IPPROTO_TCP, for Windows compatibility
Add DictCursor.dict_type to override it.
Add comment.
Python 2.6 doesn't have OrderedDict
Merge pull request #158 from methane/dict-type

Add DictCursor.dict_type to override it.
Merge remote-tracking branch 'origin/pr/140'

Conflicts:
	pymysql/connections.py
Merge remote-tracking branch 'origin/pr/148'

Conflicts:
	pymysql/connections.py
	pymysql/cursors.py
Merge pull request #150 from rfk/full-thread-id

Parse full 4-byte unsigned int for server_thread_id.
Merge remote-tracking branch 'origin/pr/156'

Conflicts:
	pymysql/err.py
Fix typo.