Remove warning compiling strsep.c

Function not previously declared warning.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Improve tdsbytes.h header

Use byteswap header even for x64 improving performances.
Add some comments.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Make display size c compliant

For now is just style, I'm planning to use to generate some C code.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Return not nullable for CHAR, BINARY and NUMERICs

is_nullable_type is used in BCP code to understand if Sybase
has to send data as part of row or variable data.
These type go to row if are not null so must return false.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Optimize is_similar_type

Remove second test does not change the results.
The reason is that if second is true the first is also true as if they are
unicode they are surely char.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>