Fix a minor bug in MSSQLConnection

Do not override callable server_version with a non-callable.

[skip ci] do not run tests - Travis doesn't have MS SQL.
Merge branch '1.5' into 1.6

[skip ci] do not run tests - Travis doesn't have MS SQL.
SQLObject 1.5.4 was released 8 Dec 2014

[skip ci]
Merge branch '1.5' into 1.6

SQLObject 1.6.2 and 1.5.4 were released 8 Dec 2014

[skip ci]
Release 1.5.4
Merge branch '1.5' into 1.6
Release 1.6.2