Remove limit(1) when calling singleResult()

In singleResult, the query will already be limited to 1 result
Fix logarithm functions MSSQL Server

Add MSSQL Server's LOG() function to SQLServerTemplates
Fix Math tests MSSQL Server
Fix Math tests Firebird
Merge pull request #993 from querydsl/firebird-math-test

Fix Math tests Firebird
Merge branch 'master' into i990
Merge pull request #994 from querydsl/single_result

Remove limit(1) when calling singleResult()
Merge pull request #992 from querydsl/i990

Register MSSQL Server specific math functions