janitorial: fixed certain whitespace issues

Removed trailing blank lines, removed tabs, etc.
cursor: comprehensions for faster row values
connection: minor startup optimizations

Leveraged pythonic patterns to reduce the amount of logic
startup_connection() executes to handle the 'database' connection
option, while preserving the same behavior.  Removed an unnecessary/
redundant initialization of the local message variable. Removed an
unused import.
column: minor data type conversion optimizations

Changes the data-type conversion mapping from a list of lists to
a list of tuples, increasing efficiency and clarity.
connection: more pythonic language

Leverages dictionary's setdefault() method to improve readability
and performance of connection initialization.  Removes treatment
of unused 'row_style' parameter.
connection: fix exceptions thrown trying to close unconnected sockets

There are places where exceptions can be thrown during connection,
these are caught and as part of cleanup, close_socket() is invariably
called.  If (and this happens) the socket has not been setup at this
point, then an unexpected error occurs and is passed to the client.
This commit attempts to close the socket iff it exists at the point of
error, allowing the client access to the actual connection exception/
error.  It also removes resetting the socket attribute, since this is
taken care of in the call to reset_values().
Merge pull request #39 from uber/hardening

Hardening