ReaderImplBase: Fix gcc 4 build
PackageFileHeapWriter: Add error message

... in case compression fails unexpectedly.
libroot_build: Fix fs_read_attr() in fs_attr_untyped.cpp

* With a specified buffer size smaller than the attribute size the
  function would fail with ERANGE on Linux although it should just read
  as much as possible. Now we always read into our temporary data buffer
  with the full buffer size.
* Fix return value in case pos is > 0. pos must be subtracted from the
  bytes actually read.
Add padding in HPKG/HPKR headers

... so that the different alignment on 32 and 64 bit machines doesn't
change the layout.
ReaderImplBase: Fix strings subsection validity check

A strings section with 0 strings is still 1 byte long. Also improve the
error output in the error case.
packagefs: Fix debug build
Add dvprintf()
packagefs: Add va-args version ERRORV() to DebugSupport
packagefs: Resolve error output TODOs
packagefs: PackageData: Fix copy and paste error
BuildHaikuPackage rule: Add grist to package info file

... to avoids clashes with equally named targets.
Support booting with a packaged boot loader

* Add new package haiku_loader.hpkg and move haiku_loader there. The
  package is built without compression, so that the stage 1 boot loader
  has a chance of loading it.
* Adjust the stage 1 boot loader to load the haiku_loader package and
  relocate the boot loader code accordingly.