beta-4

All of the bug fixes, including regression fixes and freedos fixes.

• UMB handling in freedos got many fixes. As the result, we can
  now set a record of 332K of UMB space (with UMB at A0, among others).
  This is impossible on the original freedos, at the time of writing this.
• Crash with some versions of ld linker was fixed
• Added reboot support. This was the most difficult and intrusive
  change of this beta, even if sounds simple. :)
• Many fixes to both freedos and fdpp.