Z3c.form

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- Feature: Missing terms in vocabularies: this was a pain until now.
Now it's possible to have the same (missing) value unchanged on the object
with an EditForm after save as it was before editing.
That brings some changes with it:

* *MAJOR*: unchanged values/fields do not get validated anymore
(unless they are empty or are FileUploads)

* A temporary ``SimpleTerm`` gets created for the missing value
Title is by default "Missing: ${value}". See MissingTermsMixin.

- Feature: Split ``configure.zcml``

- Bug: ``SequenceWidget`` DISPLAY_MODE: silently ignore missing tokens,
because INPUT_MODE and HIDDEN_MODE does that too.

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- Feature: Added ``IForm.ignoreRequiredOnValidation``,
``IWidgets.ignoreRequiredOnValidation``,
``IWidget.ignoreRequiredOnValidation``.
Those enable ``extract`` and ``extractData`` to return without errors in
case a required field is not filled.
That also means the usual "Missing value" error will not get displayed.
But the ``required-info`` (usually the ``*``) yes.
This is handy to store partial state.

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- Fixed broken release, my python 2.7 windows setup didn't release the new
widget.zcml, widget_layout.pt and widget_layout_hidden.pt files. After
enhance the pattern in MANIFEST.in everything seems fine. That's probably
because I patched my python version with the \*build exclude pattern patch.
And yes, the new files where added to the svn repos! After deep into this
again, it seems that only previous added \*.txt, \*.pt files get added to
the release. A fresh checkout sdist release only contains the \*.py and \*.mo
files. Anyway the enhanced MANIFEST.in file solved the problem.

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- Feature: Implemented widget layout concept similar to z3c.pagelet. The new
layout concept allows to register layout templates additional to the widget
templates. Such a layout template only get used if a widget get called. This
enhacement is optional and compatible with all previous z3c.form versions and
doesn't affect existing code and custom implementations except if you
implemented a own ``__call__`` method for widgets which wasn't implemented in
previous versions. The new ``__call__`` method will lookup and return a
layout template which supports additional HTML code used as a wrapper for the
HTML code returned from the widget render method. This concept allows to
define additional HTML construct provided for all widget and render specific
CSS classes arround the widget per context, view, request, etc
discriminators. Such a HTML constuct was normaly supported in form macros
which can't get customized on a per widget, view or context base.

Summary; the new layout concept allows us to define a wrapper CSS elements
for the widget element (label, widget, error) on a per widgte base and skip
the generic form macros offered from z3c.formui.

Note; you only could get into trouble if you define a widget in tal without
to prefix them with ``nocall:`` e.g. tal:define="widget view/widgets/foo"
Just add a nocall like tal:define="widget nocall:view/widgets/foo" if your
rendering engine calls the __call__method by default. Also note that the
following will also call the ``__call__`` method ``tal:define="widget
myWidget"``.

- Fixed content type extraction test which returned different values. This
probably depends on a newer version of guess_content_type. Just allow
image/x-png and image/pjpeg as valid values.

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- Remove ``zope34`` extra, use an older version of z3c.form if you need to
support pre-ZTK versions.

- Require at least zope.app.container 3.7 for adding support.

- Avoid dependency on ZODB3.

- Added IField.showDefault and IWidget.showDefault
That controls whether the widget should look for field default values
to display. This can be really helpful in EditForms, where you don't
want to have default values instead of actual (missing) values.
By default it is True to provide backwards compatibility.

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- Fixed a potential problem where a non-ascii vocabulary/source term value
could cause the checkbox and readio widget to crash.

- Fixed a problem with the ``datetime.timedelta`` converter, which failed to
convert back to the field value, when the day part was missing.