swift234

Explode Algorithm.swift.gyb into separate test files

- Added CollectionType and SequenceType.swift.gyb
- Added Slice.swift.gyb
- Added a template file for shared lazy flatMap code between sequences
  and collections
- Moved some test structs into the respective Check* files in
  StdlibUnittest.
- Slice.swift.gyb is still too slow for Debug-Assert stdlib builds.
  I've added a requirement to use the optimized standard library but
  we should split this file out even further.

rdar://problem/22095015

Swift SVN r30894