Update configure.in to match what it must have said when configure was generated. One thing I should probably explain about the patch as my change may seem odd otherwise - upstream's configure.in says "USE_SVG=0" but the generated configure says "USE_SVG=1", so I've simply updated configure.in to match what it must have said when configure was generated.
Remove wxSTRING_MAXLEN (removed in wx3.0) and incomp. definition. The definition wxSTRING_MAXLEN was removed from the public API of wxWidgets. Its meaning was basically "take all the string", whenever a string length was expected. The missing definition didn't raise a compilation error because TreeLib's treedrawer.h contained a fall-back definition, which is however incompatible with the original definition of wxWidgets and therefore is interpreted by wxWidgets as a number representing the real string length. This patch gets rid of the dangerous fall-back definition and of all of its uses by using alternative wxString constructors that achieve the same behavior.
