dxf-check with r13 errors

[rurban]

dwg2dxf problems with r13 and r14:

• [x] the paper space block is listed in the BLOCK_CONTROL.entries also
• [x] the 0 layer is listed 2x in the LAYER_CONTROL.entries. Same problem with STYLE, LTYPE, ...
• [x] DICTIONARY 0.1.D and 0.1.E have no ownerhandle. All NOD dicts need owner 4.1.C
• [x] No table record object (e.g. LAYER 0) has one.
• is_xref_ref is always set, even when never referenced (r13 only). might be harmless
• [ ] ODA errors: Undefined LineType in BLOCK (e.g. LINE1)
• [x] pline order in dxf.test
• insert order in dxf.test (somehow acad/oda inserts 2 inserts, and changes all polyline handles). not a bug

e.g. ./dxf-check r13/BLANK