- Improve diagnostic output of compare() function
- Test inverted matrix times original against identity using
  element by element comparison, and use less strict tolerance
  to account for innacuracies due to matrix inversion

In some circumstances it might be NULL there.

In the input file of the aforementioned tutorial, some top-level branches
depended on another branch that determined their size for every entry
(e.g. the size of an array branch). When processing this kind of data,
branches that depend on size (or count) branches will trigger a call
to TBranch::GetEntry on the latter to ensure their size is read.

The scenario described above made the parallelization of TTree::GetEntry
thread-unsafe, since a count branch could be processed at the same time
by two tasks: its own task and the task that was processing the branch
that needed the size.

This has been solved by factoring out the count branches, which are
processed first sequentially and independently of the rest of the branches.
The latter can be processed safely in parallel afterwards because all the
sizes have been read already.

Currently, we run only a very small subset of checks (the static analysis checks).

For PRs clang-tidy reports only if the regression is triggered by one of the
modified lines.

There is a cron-job mode which is unused and it could be enabled (through travis)
in future. If enabled now, it reports multitude of issues (reports stop at 10K
lines of log due to travis limit).

* Fix for ROOT-8732 - PyROOT cannot read/write C++ class fields of Double32_t

* Try to please clang-format

* Again :-(

Addressed security threat reported by S. Luders.
Using the same technology used in TSystem::ExpandFileName (with clang-format processing).

Casting the matrices from double to float create small rounding
errors of the order of 1e-06 in the reference matrices themselves,
so when they are multiplied the sum over long rows/columns accumulates
many rounding errors and make the test fail. Using TMatrixT of float
as the reference to begin with eliminates this problem.

Often used by web browsers as default icon

Now websocket and longpoll socket can be exchanged to large extent.
Big advantage of longpoll - one could run it over fastcgi or via proxy
internet connection. Will be supported within TWebCanvas 

It uses open requests to send data directly from server.
For the moment buffers queue depth=1, but can be easily improved

THttpServer may decide to postpone reply on the requests.
Such reply can be performed later via invoking some user code.
Will be used for implementing long poll