Whitespace, 80-col violations.
Comment.
Make hostPlatform available in D.C.SetupWrapper.

Removes the uses of buildPlatform from D.C.Install.
Fix redundant imports.
Add 'buildCompiler' to Distribution.Compiler.
Append $os and $arch to the names of cached setup exes.

Fixes #1226.
Merge pull request #1227 from 23Skidoo/setup-cache-platform

Append $os and $arch to the names of cached setup exes.