Logic cleanup for REPL
Merge pull request #725 from david-christiansen/cleanup-repl-invoke

Logic cleanup for REPL
Fix too-new import

fixes https://github.com/idris-lang/Idris-dev/issues/724
Merge pull request #726 from Melvar/collections-fix

Fix too-new import
Invoke the chaser as a consequence of :l

This has also been updated for the --ideslave equivalent. Fixes #727.
Merge pull request #728 from david-christiansen/issue/727

Invoke the chaser as a consequence of :l
Rename UnusedArgs to Erasure.
Remove export of traceUnused.
Simplify unused arg search.
Cleanup and purification in Erasure.hs.
More purification.
Simplification with pattern guards.
findUsed stub written.
Make ProjCase take exactly one alternative.   (TODO: is this safe?)