* Added lex_yacc module.
* Introduced property cpp.systemRunPaths.
* Introduced the ability to check a module's version in a Depends item.
* Introduced cpp.driverFlags, which allows specifying flags to be
  passed to the compiler driver (in any mode), but never the system linker.
* Introduced cpp.linkerMode property to allow selection of the
  correct linker (C driver, C++ driver, or system linker) based on the
  objects being linked.
* Added automatic escaping of arguments passed to the
  cpp.linkerFlags and cpp.platformLinkerFlags properties using the -Wl
  or -Xlinker syntaxes. To revert to the old behavior,
  Project.minimumQbsVersion can be set to a version lower than 1.6.
* Each build configuration now requires a unique name, which
  is specified on the command line in the same place that qbs.buildVariant
  used to be specified. This allows building for multiple configurations
  with the same variant.
