Fix unexpected behavior of --deblock option.
Fix unexpected behavior of --deblock option.

Giving a single number as an argument to --deblock option would enable
deblocking and set both beta and tc to that value. This commit changes
a single number argument to be interpreted as a boolean specifying
whether to enable deblocking or not. As a result, "--deblock 0" can be
now used to disable deblocking.

This fixes deblocking being enabled in all presets.

ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar