Par-Test allows redefinition of srcDir by Ant

Since srcDir is no longer used to extract the test kind from any
given test path, it is especially benign to rely on the defness
of srcDir in order to allow redefinition during an Ant run.

The parameter is configured via the partest.srcdir property.

Maybe the keyword should be def for definite values and
red for redefinable values and ind for indefinite values.
And ded for dedefinable values optionally reset to None.
Disabled failing bitset test.

It's a couple orders of magnitude out of whack when a test
demands a gigabyte of memory to pass. We might need to start
collecting per-test stats to avoid this kind of thing in the
future. It's a huge waste of time.
Merge pull request #2438 from paulp/pr/bitset-test

Disabled failing bitset test.
SI-7402 List extends Serializable

While we are all aware of the issues around Serialization,
I think in this case it is perfectly sound and safe to make
List serializable:

- List is not an interface, it is the base type of an ADT.
  Common behavior of its members should be reflected in the base type.
- List is sealed, there is no chance of an user providing a new
  non-serializable subtype of List.
Merge pull request #2431 from som-snytt/issue/partest-srcdir

Par-Test allows redefinition of srcDir by Ant
Merge pull request #2441 from soc/SI-7402

SI-7402 List extends Serializable