Add optional task signatures to buildhistory

If you're looking to compare task signatures between builds, that can actually be a bit difficult to do if you don't have anything printed out (e.g. from an error) with some signatures to look for. buildhistory already makes a commit (or several commits) for each build, so we can actually write the signatures into buildhistory so that we can compare them later. If available (via the tasks actually having run, or by explicitly creating them), we can even use the siginfo/sigdata files to dig down and find out exactly what caused the signature changes.

Finally, add sha256sums for each file staged by every shared state task so that we can see when a task re-executes if the file contents has changed.

(All of this functionality defaults to off, you need to add "task" to BUILDHISTORY_FEATURES in order to enable it).

There's also a small fix making it a bit easier to run the buildhistory-diff script from the buildhistory repository.

NOTE: this patch series requires some of the patches in the set recently sent to the bitbake-devel list.

The following changes since commit 901659a51cd53625a93f57a9c5865e90a07ec09d:

oeqa/runtime/utils/targetbuildproject: use parent classes defaults tmpdir (2017-04-06 10:13:34 +0100)

are available in the git repository at:

git://git.openembedded.org/openembedded-core-contrib paule/buildhistory-sigs
http://cgit.openembedded.org/openembedded-core-contrib/log/?h=paule/buildhistory-sigs

Paul Eggleton (6):
buildhistory-diff: operate from buildhistory directory classes/buildhistory: write out task signatures on every build
buildhistory-diff: add option to compare task signature list
buildhistory-diff: add option to compare actual signature differences classes/uninative: set SSTATEPOSTUNPACKFUNCS[vardepvalueexclude] properly classes/buildhistory: save output file signatures for sstate tasks

 meta/classes/buildhistory.bbclass    |  40 +++++++++++++
 meta/classes/uninative.bbclass       |   2 +-
 meta/lib/oe/buildhistory_analysis.py | 109 ++++++++++++++++++++++++++++++++++-
 meta/lib/oe/sstatesig.py             |  10 ++++
 scripts/buildhistory-diff            |  13 ++++-
 5 files changed, 170 insertions(+), 4 deletions(-)

2.9.3