Attempt at PartitionedGuidedImprovementAlgorithm.

In this implementation, the search space is split into separate and
independent partitions, based on the first Pareto point found.

This implementation works for any number of objectives. Single-objective
problems are special-cased, since partitioning doesn't make sense.

Tasks are submitted to a threadpool only if its dependencies have
completed. The search space is only split on the first Pareto point; the
subtasks will not recursively split their partitions.
Clean up whitespace
Clarify comments about mapping bitset bits to metrics, and iterating over objectives.
Rename PartitionedSearcher to PartitionSearcherTask. Change from Callable<Formula> to Runnable
Use a CountDownLatch to wait for tasks to complete, instead of blocking on a queue of futures
Consolidate both for loops in the linkDependencies method
Clean up some of the logging in PGIA
Merge branch 'master' into amalgam-partitioned-gia

Conflicts:
	src/kodkod/multiobjective/MultiObjectiveSolver.java
Throw an exception if the objectives aren't sorted

This is for the set of objectives in the partitionConstraints method,
since it requires the order to be deterministic. Sorting is a sufficient
(but not necessary) condition for this.
Remove unused import
Remove boundary finding from PGIA and fix some code review comments
Set LD_LIBRARY_PATH when to point to the libs.
Address code-review feedback.
Merge pull request #52 from TeamAmalgam/ci-with-libraries

Use native solver libs when running unit tests
Adds arguments support for moolloy
Merge pull request #39 from TeamAmalgam/amalgam-checkpointing-clean

Add Checkpointing Support to Kodkod
Merge pull request #40 from TeamAmalgam/amalgam-partitioned-gia

Implement PartitionedGuidedImprovementAlgorithm
Merge branch 'master' into amalgam-moolloy-arguments

Conflicts:
	src/kodkod/multiobjective/MultiObjectiveSolver.java
Merge pull request #53 from TeamAmalgam/amalgam-moolloy-arguments

Adds arguments support for moolloy
Added solution logging to PGIA.