Group "last message repeated N times" in syslog output for baselines

[noproto]

The whitebeam --baseline output includes superfluous syslog artifacts.

Erroneous output:

| Detection: /usr/bin/apt wrote to /var/lib/apt/lists/partial/ (VerifyCanWrite)                                                                                                         | 10    |
| message repeated 2 times: [ Detection: /usr/bin/apt wrote to /var/lib/apt/lists/partial/ (VerifyCanWrite)]                                                                            | 1     |

Expected output:

| Detection: /usr/bin/apt wrote to /var/lib/apt/lists/partial/ (VerifyCanWrite)                                                                                                         | 12    |

If a line starts with "message repeated", it should be added to the total observed count of the relevant event.