Add function to drop individual table.  Refactor droptables to keep single codebase.
"MySQLDialect.CreateTableSuffix()" now panics if called with uninitialized values
Adds a SetUniqueTogether method on TableMap.

SetUniqueTogether adds uniqueness constraints across multiple columns
of a table. Much like setting a single column as unique, this
constraint is used *only* during table creation and not during
insert/update. SetUniqueTogether may be called multiple times, which
sets additional constraints.
Remove accidental "t.Error(err)" at the end of the SetUniqueTogether test
Merge branch 'mysqlDialectPanic' of https://github.com/LeGEC/gorp into LeGEC-mysqlDialectPanic
TestWithTimeSelect: add 1 second to w2 row to avoid timing issues with mysql
Merge branch 'unique-together' of https://github.com/Nitron/gorp into Nitron-unique-together
generalize trace logging mechanism
Add docs about GorpLogger interface
Return a sql.ErrNoRows when SelectOne does not return any row.

The SelectOne wants to return just one row, so it should also return an error
when no rows were returned. In this case, this function will return an
sql.ErrNoRows, as it's done in some functions of the database/sql package.
minor doc change on SelectOne() in readme
Merge branch 'release/v1.3'