Only run "set term=..." when not set correctly

    Putting set term=... when $TERM was already equal to xterm-256color
    appears to cause issues that prevent any color from working
    properly.
Condition now identifies OS correctly

    The conditional statements were intended to determine if has('unix')
    is true, but due to some mispaced operators, would return true for
    has('win32unix') and has('win32'), preventing the plugin from
    loading correctly on systems it's compatible with.
Corrected the 'do' argument for a plugin's hook