This can cause bugs where if the operator throws an exception, undo is not
properly enabled again. There have been maybe a dozen Blender bug reports
related to this. This could get worse now that we are autosaving preferences.

Some add-ons guard against this, but turning off undo should not be needed in
the first place. If the operator is set to do an undo push, any operators it
calls will automatically not do any undo pushes.

If this fail in some cases, it should be reported as a bug in Blender. I could
not find issues or a performance impact testing a few add-ons though.

Differential Revision: https://developer.blender.org/D4908

Addresses new behavior of object.to_mesh().

This is corresponding part for D4875.

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D4876

Mainly search-and-replace approach.

Tested the enabled-by-default export/import addons. Seems to work with
an exception of X3D which is still referencing Blender Internal material
properties.

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D4866

Grease pencil must have name 'GPencil'.
Script take only the first strokes.

own recent error in rBA73f88be5067b

also fix matrix multiplication ('@')

Fixes T60706

followup to rBA3148c4219f001511b69c3fb31dfedca98b9f4360

Fixes T58714

This ports the already working addons. The disabled x3d, psk, lwo, 3ds,
raw, dxf addons still need to be converted.

Bumped version to 4.6.7
As a part of the task T50726:
Update the Panel rename code to more generic one

PEP8 cleanup:
Tuple imports and use them for class types
Consistent Scene props definitions
Update url link

This only fixes the 'symptoms', root of the issue here is that we get
a weird covariance matrix - Blender's own invert function errors on it,
this script's matrix_invert func does give some result, but in any case
final result is not what one would expect...

Fix error reported by talocan. Gstretch function was not calling ensure_lookup_table, see rB785b90d7ef

Please don't add API versions all over scripts,
having API versions over function calls isn't helping make code readable,

No need to document the API in scripts unless there is some exceptional case worth noting.

#    blender 2.73 needs to call ensure_lookup_table() for bm.verts[], bm.edges[], bm.faces[].
#    generically the fix will do this...
#    the lookup_table will get "dirty" after:
#    bm.new(), bm.from_mesh(), bm.from_edit_mesh()
#    bm.verts.new(), bm.edges.new(), bm.faces.new()
#    bm.verts.remove(), bm.edges.remove(), bm.faces.remove()
#    bm.normal_update(), bm.copy()
#
#    bm.verts.ensure_lookup_table() ### 2.73
#    bm.edges.ensure_lookup_table() ### 2.73
#    bm.faces.ensure_lookup_table() ### 2.73

#    blender 2.73 has a new grease_pencil per object and new per scene
#    gp = object.grease_pencil
#    if not gp:
#        gp = context.scene.grease_pencil

Checking for zero-length vector wasn't sufficiently robust.
Could result in NaNs being assigned to vertex coordinates.

Merge of soc-2013-paint added a new parameter to strokes: "size"
This crashed the add-on when trying to erase strokes (since they
did not yet have this additional parameter)

Makes conversion of grease-pencil strokes more robust.