Fix insert/erase notifications in InfTextFixlineBuffer
Fix insert/erase notifications in InfTextFixlineBuffer

The notifications were missing when the fixline buffer was modified directly
with the API, and not in response to modifications to the underlying base
buffer.

gobby/libinfinity,gobby/libinfinity,tyll/libinfinity,tyll/libinfinity,tyll/libinfinity,gobby/libinfinity