Update to upstream version jdk8u20-b18

Patches in debian/patches have been changed/refreshed as follows:

Deleted:

sparc-stubgenerator.diff
	(has been added upstream in a slightly different form)

Adapted to changes in upstream code:

accessible-toolkit.patch
hotspot-powerpcspe.diff
system-lcms.patch

Adjusted to new offset in upstream code:

default-jvm-cfg-default.diff
dnd-files.patch
fix-jtreg-location.patch
hotspot-sparc-arch.diff
ld-symbolic-functions-default.diff
system-libjpeg.patch
system-libpng.patch

Whitespace change in patch formatting:

zero-missing-headers.diff