Correct tab completion of the dump command commandline

[peterbarker]

Imagine the <tab><tab>s in the following:

MAV> dump 
AHR2     DU32     IMU      MAVC     NKF3     NKQ2     PAY5     SRTL
ATT      EV       IMU2     MAV[3]   NKF4     NKT2     PM       TERR
BAR2     FMT      IMU3     MODE     NKF5     ORGN     POS      UNIT
BARO     FMTU     ISBD     MOTB     NKF6     PARM     POWR     VIBE
BAT      GPA      ISBH     MSG      NKF7     PAY1     PPO2     __MAV__
CMD      GPS      MAG      MULT     NKF8     PAY2     RATE     
CTUN     GUID     MAG2     NKF1     NKF9     PAY3     RCIN     
DSF      HEAT     MAV      NKF2     NKQ1     PAY4     RCOU     
MAV> dump I
IMU   IMU2  IMU3  ISBD  ISBH  
MAV> dump I