ogr_autocad_services.cpp has incorrect logic on a C++14 compiler

[etresoft]

The C++ std::string::assign method has changed in C++14. The ACAdjustText method is relying on cast to a C string in its assign operations. While ogr_autocad_services.cpp still compiles, but now uses a different assign method resulting in incorrect logic. I found the error while building and testing GDAL on Xcode 6.3.2. I am building the 1.11.2 branch, but the same logic seems to be present in the 2.0 branch.

[etresoft]

Patch file for C++ compatibility.

[etresoft]

PS: I was comparing tests against Linux running Ubuntu 14.04. The new code doesn't seem to have broken the Linux build.

[Even Rouault]

trunk r29363, branches/2.0 r29364 (post RC2) "DXF: make it compatible with C++11/C++14 (patch by etresoft, #6002)"

[Even Rouault]

Post analysis: the issue is with C++14 only.

The culprit here is was our use of the CPLString class extending std::string with a implicit conversion operator to const char*.

Previously string& assign (const char* s, size_t n) was used when a CPLString was passed. But in C++14, string& assign (const string& str, size_t subpos, size_t sublen = npos) was now used since the sublen argument became optional.