[mingw32-qt/f15] (6 commits) ...Update to 4.7.4

[epienbro]

Summary of changes:

  4a91900... Rebuilt with mingw32-libjpeg-turbo, dropped jpeg_boolean pa (*)
  89c074b... Update to 4.7.3 (*)
  8b4284b... Spec clean up (*)
  2047a9e... Enable the float.h using code again (*)
  6c4ae8c... Avoid including .dll.debug files in the main package (*)
  dc39f8a... Update to 4.7.4 (*)

(*) This commit already existed in another branch; no separate mail sent