#16 Fix mysql backend compilation on MSVC (2008 and 2012 tested)

[Mingun]

Fix following compilation error:

[  3%] Building CXX object CMakeFiles/cppdb.dir/drivers/mysql_backend.cpp.obj
mysql_backend.cpp
<mysql-include>\mysql_com.h(315) : error C2146: syntax error: missing ';' before identifier 'fd'
<mysql-include>\mysql_com.h(315) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int