1.7.2

CHANGES:

• Add ${corrected-suffix}, ${library-name} and a few other
  variables to the list of variables to upgrade. This fixes the
  support for various framework producing corrections (#1840, #1853,
  @diml)

• Fix $ dune subst failing because the build directory wasn't set. (#1854, fix
  #1846, @rgrinberg)

• Configurator: Add warning to Pkg_config.query when a full package expression
  is used. Add Pkg_config.query_expr for cases when the full power of
  pkg-config's querying is needed (#1842, fix #1833, @rgrinberg)

• Fix unavailable, optional implementations eagerly breaking the build (#1857,
  fix #1856, @rgrinberg)