Fix CDC auto-reset for Mac OSX

The OSX USB driver apparently behaves differently than other platforms
with regard to baud rate and DTR handling.  This fix forces DTR low for
1 second in ard-reset-arduino to guarantee that Cosa will reset
regardless of host platform behavior.  Also corrected a comment about
the watchdog time to match the wdt_enable.
Merge pull request #258 from jediunix/CDC-auto-reset-osx-fix

Fix CDC auto-reset for Mac OSX