MAINT some more pointer safety in LibSVM

All pointers are asigned to NULL after delete
and are checked not NULL before reference in
svm_free_and_destroy_model and svm_free_model_content.

Conflicts:
	sklearn/svm/src/libsvm/svm.cpp
MAINT import LibSVM 310

version number changed to 310

Conflicts:
	README
	java/libsvm/svm.m4
add a comment for sigmoid_predict in svm.cpp
MAINT import LibSVM patch from upstream

int i; in svm_predict_values for openmp

Conflicts:
	sklearn/svm/src/libsvm/svm.cpp