release-0.17.1

• Made forge adopt reliably adopt CMake interface libraries that publish
  headers from source roots such as src/, while excluding optional CMake
  subprojects and their unrelated dependencies.
• Added public-header validation entry points. Header-only packages can keep
  their complete installed header tree while validating an aggregate umbrella
  header when individual leaf headers are not standalone entry points.
• Made CMake project-source variables and optional __has_include branches
  resolve without producing false dependency suggestions. Source-root headers
  are packaged beneath the conventional include/ directory in cboxes.