DXF: Incorrect text escaping behaviour

[Alan Thomas]

The behaviour of AutoCAD is to apply %%d, %%c and %%p escapes in the text content of TEXT, MTEXT and DIMENSION objects only. Additionally, backslash escapes like \P and \~ only work on MTEXT objects. Layer names and the like do not honor any escapes

See the attached DXF file, screenshot and patch. ogrinfo currently issues the following output for this DXF file:

OGRFeature(Entities):0
  OGR_GEOMETRY (String) = POINT
  Layer (String) = MyLayer°∅
  SubClasses (String) = AcDbEntity:AcDbText:AcDbText
  EntityHandle (String) = EEEF0
  Text (String) = singleline%%D∅\\P\Pmore\~text
  Style = LABEL(f:"YourTextStyle°∅",t:"singleline%%D∅\\P\Pmore\~text",p:1,s:1g,c:#000000)
  POINT Z (0 0 0)

OGRFeature(Entities):1
  OGR_GEOMETRY (String) = POINT
  Layer (String) = MyLayer°∅
  SubClasses (String) = AcDbEntity:AcDbMText
  EntityHandle (String) = EEEEF
  Text (String) = multiline°∅\P
more text
  Style = LABEL(f:"Arial",t:"multiline°∅\P
more text",s:1g,p:7,c:#000000)
  POINT Z (0 5 0)

The layer name and contents of the TEXT object are incorrect.