Promoting 2.014.17 as 2.015. Since 2.014, we have the following improvements: * Portability: support cormanlisp, xcl; fixes for cmucl, ecl; tweaks for abcl, allegro, clisp, genera, lispworks. * Feature: un-cerror and actually fix the :force '(sys1 sys2 sys3) feature, introduced in 2002 and never working before. * Feature: classes asdf:cl-source-file.cl and asdf:cl-source-file.lsp for people who use these file type extensions. * Semantic change: the source-registry eagerly gathers a list of .asd, rather than querying the filesystem over and over again. * API change: exposing function asdf:search-for-system-definition as looking through asdf:*system-definition-search-functions* for either pathnames *or* (new feature) system objects. Should make quicklisp happier. * Better support for asdf upgrading itself, with new function asdf:upgrade-asdf that knows to invalidate old systems when necessary, and is magically invoked before to build any system that :depends-on asdf. Make upgrade smoother some cases that were previously broken. * More robust handling of version strings. * Declaring function asdf:system-definition-pathname obsolete, but still supporting it for now, as an alias for asdf:system-source-file. * Various refactorings of internals. Splitting a function asdf::perform-plan out of the default asdf:operate method. asdf::register-system now takes only one argument. * Tests to prevent the regressions experienced during this development cycle * Tried and reverted: attempts to make asdf more verbose when it's verbose, but not verbose by default.