Since .data can be BTreeData or None (or as we'll see next and str),
._p_mtime() is not always defined on it and in several places current
code has branches from where to get it.

Move this logic out to a separate helper and the code which needs to
know mtime gets streamlined.
Suggested-by: Vincent Pelletier <vincent@nexedi.com>

Because we next pass that btree to ._read_data() and read_data()
intentionally creates empty BTreeData() when btree is initially None.
Reviewed-by: Romain Courteaud <romain@nexedi.com>

If in erp5 I go to big_file_module and 'Add Big File' action and then try to
download just-created empty bigfile I get a crash:

    curl ... --data 'format=raw'  http://localhost:8889/erp5/big_file_module/18

    ...
    <h2>Site Error</h2>

    <p>An error was encountered while publishing this
     resource.</p>

    <p>
      <strong>Error Type:
        AttributeError
      </strong>
      <br />
      <strong>Error Value:
        'str' object has no attribute 'iterate'
      </strong>
      <br />
    </p>

with exception traceback

    Traceback (innermost last):
      Module ZPublisher.Publish, line 138, in publish
        request, bind=1)
      Module ZPublisher.mapply, line 77, in mapply
        if debug is not None: return debug(object,args,context)
      Module ZPublisher.Publish, line 48, in call_object
        result=apply(object,args) # Type s<cr> to step into published object.
      Module Products.ERP5.Document.BigFile, line 297, in index_html
        for chunk in data.iterate():
    AttributeError: 'str' object has no attribute 'iterate'

I've compared BigFile code with the sample place in File code from Zope/src/OFS
(which is base class for BigFile)

    https://github.com/zopefoundation/Zope/blob/2.13/src/OFS/Image.py#L420

and in index_html(), if we requested the data itself, there it sees whether
self.data is either

    1) simply bytes (= str in python2), or

    2) linked-list of Pdata

and in BigFile we currently miss handling 1) case.

~~~~

BigFile, it looks, was copied-and-modified from Zope.OFS.Image.File first in
65121be7 (Support streaming big file in DMS.) Then in index_html download there
was only an 'iterate over btree chunks' case. Later in dff53681 (Get
modification date from btree.) a case for

    if data is None:
      return ''

was added before btree iteration.

Here we also restore original Zope code for returning file content if it is
string instance directly, because as it is experimentally observed, that case
can also happen.

The patch does not add tests, because currently BigFile class does not have
tests at all (at least I could not find them).
Reviewed-by: Romain Courteaud <romain@nexedi.com>

This reverts commit 2a061744.

An outdated customization of Base_getEditorFieldPreferredTextEditor on
our ERP5 introduced confusion

In testInventoryAPI we test several cases of getNextNegativeInventory.
Remove this test which is long, hard to understand, and only test
a case that is not really making sense (current stock with negative
inventory)

This avoid differences like 07:55:27 != 07:55:26 in tests

the display of this form was broken

This is needed to take into account the node when looking at the history
of movements

So all newSimulation expected failures are removed. Make
generateMovementListForStockOptimisation looking min_flow and max_delay
on supply lines.

Introduce a getNextAlertInventoryDate in addition to
getNextNegativeInventoryDate. This allows to know when an inventory
will be below a reference quantity. This is particularly helpful
to know when an inventory is below the minimal admitted stock

So it's no longer a newSimulation expected failure. Review method
generateMovementListForStockOptimisation of builders to nicely
generated temporary movements depending on future negative stocks.

Like this we stop using Resource_zGetInventory which is less
and less used. Indeed, it's better to only have Resource_zGetInventoryList
and sometimes returns a list of a single line.

Now production steps are defined in business process which
are using trade_phase. indistrial_phase was used at the time
of supply chains

MRP was broken and unused for a long time, since legacy simulation was dropped.
This commits resuscitates MRP, at least:
- expanding, for both operation and sourcing
- building of production reports & production packing lists

Business Processes replaces Supply Chains.
trade_phase replaces industrial_phase
industrial_phase is now used to variate partially produced resources.