ob-sql.el: Support sqlcmd in Cygwin environment

ob-sql.el: Support sqlcmd in Cygwin environment

* lisp/ob-sql.el (org-babel-sql-dbstring-mssql): Format Microsoft
  `sqlcmd' command line args.
(org-babel-sql-convert-standard-filename): Convert a Posix path to
Windows long path in Cygwin environment, or do nothing.
(org-babel-execute:sql): Add `mssql' engine support and remove support
for `msosql' engine.

The `osql' command line tool was last updated in 2004,
https://technet.microsoft.com/en-us/library/aa214012(v=sql.80).aspx, and
could not output the query result in a way that morden `org-table.el'
expects.  The `sqlcmd' is the preferred command line tool to connect the
Microsoft SQL Server and it also has a Linux version,
https://msdn.microsoft.com/en-us/library/hh568447(v=sql.110).aspx.

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