Patcher bugs

[Ben Wing]

Didier -- every time I use patcher to commit a file, it inserts the [COMMIT]
at the beginning of the buffer, not in the Subject line.

Could you look into this?

The buffer ends up with a whole bunch of patcher-subject-prefix extents at
[1, 1) as well as a bunch more at the location of the [PATCH] string.

It seems wrong that there are bunches of them.  Even in a fresh patcher
buffer there are 7 or 8 patcher-subject-prefix extents at the same place.