Foreign types and variables in `extra_references` attribute

[BDanAnd]

This series of patches adds the ability to use types and variables from other modules as extra dependencies.

v3

• the local variable chunks generation attempt error message: Try -> Attempt
• clarify comments

v2

• Improve variables chunk generation in ChunkGenerator.provide_chunks.
• Properly register global variable in TestOpaqueCode test.

v1.1

• Fix the bug with duplicating entries in TypeContainer.__type_attributes__ resulting in too slow operation on real projects.
• ChunkGenerator.provide_chunks pops stack before extra_references processing. That fixes incorrect behavior of "main" if block of that method which depends ot stack during recursive calls.
• Squash some extra_references processing patches.
• Optimize TypeContainer.

[laerreal]

v1.1 is ready.

There is a problem with foreign_gl global in the test. It's never defined (only declared in the "foreign_gl.h"). As a result, it comes in provide_chunks with None definer (passed by extra_references handling algorithm for gl). It's actually a logical error in the model definition. Should we raise an exception in such a situation? Note that TypeFixerVisitor does handle Types only. So foreign_gl is not added to "testextrareferences.c" automatically when gl variable is added to the module. Looks like TypeFixerVisitor should add globals too. As a result, foreign_gl is defined (chunk only, not logically) in "testextrareferences.c" because extra_references handling algorithm works quite straightforward. It definitely should not work correctly on incorrect data (foreign_gl's definer is None).

What do u think?

[BDanAnd]

v2 is ready.

[laerreal]

v3 is ready. Merge it by self if the changes are ok.