Added %progress for sane lexical shadowing of progress in src/conditions.lisp

This allows lexically shadowing `progress' for user code (as done in
`with-sequence-progress') without making its functionality
unavailable (available by calling `%progress').

* src/conditions.lisp (%progress): new function; same as former
  `progress'
  (progress): call `%progress'
  (progressing): use `%progress'
* src/macros.lisp (header): updated copyright
  (with-trivial-progress):  use `%progress'
  (with-sequence-progress): likewise
Generate initial 0 progress event in with-sequence-progress in src/macros.lisp

* src/macros.lisp (with-sequence-progress): generate initial 0 progress
  event
* test/macros.lisp (test with-sequence-progress.smoke): adjusted number
  of expected progress conditions