build: Make sure historical release notes end up in distributions

Adds the historical release notes to release tarballs and windows
installers.
Limit the number of orphan blocks

In case the total number of orphan blocks in memory exceeds a limit
(currently set to 750), a random orphan block (which is not
depended on by another orphan block) is dropped. This means it will
need to be downloaded again, but it won't consume memory until then.
Typo fix: `anonimized => anonymized` + `infromation => information`
Merge pull request #3627 from calvintam/fix_typos

Typo fix: `anonimized => anonymized` + `infromation => information`
-Wl,-z,relro and -z,now were wiping out environmental LDFLAGS passed in by the user.
I moved them to HARDENING_* where they belong.
Merge pull request #3634

505867a -Wl,-z,relro and -z,now were wiping out environmental LDFLAGS passed in by the user. I moved them to HARDENING_* where they belong. (Midnight Magic)
Update the address for downloading libpng

The FTP server what we get libpng from only keeps the latest version in its main folder. Older versions are in the "history" folder. Apparently version 1.6.9 has been released, so 1.6.8 has moved to the history folder.
Merge pull request #3635

12edce5 Update the address for downloading libpng (Micha)
Merge pull request #3608

de21e8f build: Make sure historical release notes end up in distributions (Wladimir J. van der Laan)
doc: add preliminary release notes for 0.9.0
Cleanup v0.9 release notes
Merge pull request #3642 from petertodd/v0.9-release-notes-formatting-fixes

v0.9 release notes formatting fixes
Merge pull request #3609 from sipa/limitorphanblocks

Limit the number of orphan blocks in memory
Copyright header update, s/2013/2014