Improve T-SQL syntax highlighting

[jamend]

These changes fix overly-aggressive keyword highlighting and add several missing T-SQL keyword/function/stored procedure names (contributed by Aaron Bertrand). These changes were part of a Stack Overflow answer, and it was suggested that the changes be contributed to the project. See Improve GeSHi syntax highlighting for T-SQL

[BenBE]

There are some issues according to the langcheck script (in contrib) Could you try to correct them first?

Validating language file for 'tsql' ...     Failed

WARNING Language file contains per-group duplicate keyword '@@language' in $language_data['KEYWORDS'][1]!
WARNING Language file contains per-group duplicate keyword 'datefromparts' in $language_data['KEYWORDS'][1]!
WARNING Language file contains per-group duplicate keyword 'user_name' in $language_data['KEYWORDS'][1]!
WARNING Language file contains per-group duplicate keyword '@@identity' in $language_data['KEYWORDS'][1]!
WARNING Language file contains per-group duplicate keyword 'smallint' in $language_data['KEYWORDS'][2]!
WARNING Language file contains per-group duplicate keyword 'hadr' in $language_data['KEYWORDS'][2]!
WARNING Language file contains per-group duplicate keyword 'columns' in $language_data['KEYWORDS'][4]!
WARNING Language file contains per-group duplicate keyword 'parameters' in $language_data['KEYWORDS'][4]!
WARNING Language file contains per-group duplicate keyword 'sequences' in $language_data['KEYWORDS'][4]!
WARNING Language file contains per-group duplicate keyword 'tables' in $language_data['KEYWORDS'][4]!
WARNING Language file contains per-group duplicate keyword 'views' in $language_data['KEYWORDS'][4]!
ERROR   Language file contains no $language_data['URLS'] specification for keyword group 5!
ERROR   Language file contains no $language_data['URLS'] specification for keyword group 6!
ERROR   Language file contains no $language_data['URLS'] specification for keyword group 7!