UNKNOWN and unknown in accepable units list

[crotwell]

Given capitalization of units only results in a warning, having both unknown and UNKNOWN is redundant. UNKNOWN should not be in the list.

java -jar stationxml-validator-1.7.1.jar --units
===============================================================
|                  Table of Acceptable Units                   |
===============================================================
          meter              us     hectopascal              nT
         meters      nanosecond    hectopascals          strain
              m     nanoseconds             hPa             m/m
            m/s              ns             bar       m**3/m**3
         m/s**2          minute        millibar           cm/cm
     centimeter         minutes       millibars           mm/mm
    centimeters             min            mbar           um/um
             cm            hour          ampere           nm/nm
           cm/s           hours         amperes     microstrain
        cm/s**2          radian               A            watt
     millimeter         radians        milliamp           watts
    millimeters             rad       milliamps               W
             mm     microradian              mA       milliwatt
           mm/s    microradians            volt      milliwatts
        mm/s**2            urad           volts              mW
        mm/hour      nanoradian               V             V/m
     micrometer            nrad       millivolt          W/m**2
    micrometers           rad/s      millivolts hit/(cm**2*hour)
             um        rad/s**2              mV             gap
           um/s          degree       microvolt          reboot
        um/s**2         degrees      microvolts            byte
      nanometer             deg              uV           bytes
             nm          kelvin             ohm             bit
           nm/s               K           hertz           bit/s
        nm/s**2         celsius              Hz         percent
         second            degC          newton               %
        seconds         candela         newtons           count
     nanometers              cd               N          counts
    nanoradians          pascal           joule          number
           bars         pascals          joules        unitless
              s              Pa               J         unknown
    millisecond      kilopascal           tesla         UNKNOWN
             ms     kilopascals               T                
    microsecond             kPa       nanotesla                
===============================================================