Testmill

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* Fix but in which() on Windows. This would prevent first-time
users to use TestMill on Windows.
* Added an interface that makes it easy to use TestMill as a
library from Fabric.

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* Fix an important bug that would prevent first-time users from
using TestMill due to an issue with keypair generation.

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* Always publish to Amazon. Amazon is preferred because it allows us
to stop instances rather than kill them.
* Allow specification of the memory size for the VMs. The default is
2048 MiB.
* Allow specification of the number of CPUs.
* Add basic mercurial support (no parsing of .hginore files yet).

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* Fix a rather serious bug that could cause a deadlock in certain
situation when a task failed.
* Improve the quick start in the documentation.

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* Fix an issue where the installer doesn't download all the required
dependencies.
* Fix a critical issue where our shell glue (runtask.sh and preininit.sh)
don't get installed.
* Some fixes in the test suite.

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* Many bug fixes.
* Greatly improved test coverage.