We store `Seq[xsbt.api.Compilation]` in `Analysis`. Compilation are
being appended to sequence for every iteration of the incremental
compiler.
Note that `Compilation`s are never removed from the sequence unless
you start from scratch with empty `Analysis`. You can do that by using
sbt's `clean` command.
The main use-case for using `compilations` field is to determine how
many iterations it took to compilen give code. The `Compilation` object
are also stored in `Source` objects so there's an indirect way to recover
information about files being recompiled in every iteration.
Since `Analysis` is persisted you can use this mechanism to track entire
sessions spanning multiple `compile` commands.
Grzegorz Kossakowski