MAINT remove some dead code from the LibSVM wrapper

We ship a hacked-up v300 and won't support an older version anyway.
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
Merge pull request #2673 from larsmans/libsvm-310

MAINT update LibSVM to version 310