2.122: changes requested by sds.

* use only one package for everything: ASDF. This simplifies the upgrade a bit.
* export component-visited-p, record an index rather than a boolean.

Also
* On CLISP, only use custom:*module-provider-functions* when defined (2.49+)
* In Makefile, mrproper before debian package.
* Document that CLISP and SCL now support REQUIREing through ASDF.
* Fix mistake in run-tests that made it always use sbcl