The C++ importer incorrectly treated the contents of all TEXT and MTEXT
objects as beind encoded as UTF-8, but this is not true for DXF files
before AutoCAD 2007, where the encoding is "plain ASCII" plus some in-band
\U+dddd encoding. This would cause errors if the text contained non-ASCII
characters such as the Degree Sign.
This change causes the correct encoding to be used.
dbf17376b7