Keep SVMProblem from being garbage-collected

[dmsc]

From libsvm help:

NOTE Because svm_model contains pointers to svm_problem, you can
not free the memory used by svm_problem if you are still using the
svm_model produced by svm_train().

This causes LIBSVM package to randomly fail if julia garbage-collects the SVMProblem and nodes before calling svmpredict.

This patch solves the isue:

diff --git a/src/LIBSVM.jl b/src/LIBSVM.jl
index f50b760..b1d72e5 100644
--- a/src/LIBSVM.jl
+++ b/src/LIBSVM.jl
@@ -66,6 +66,9 @@ end
 type SVMModel{T}
     ptr::Ptr{Void}
     param::Vector{SVMParameter}
+    problem::Vector{SVMProblem}
+    nodes::Array{SVMNode,2}
+    nodeptr::Vector{Ptr{SVMNode}}
     labels::Vector{T}
     weight_labels::Vector{Int32}
     weights::Vector{Float64}
@@ -224,7 +227,7 @@ function svmtrain{T, U<:Real}(labels::AbstractVector{T},
     ptr = ccall(svm_train(), Ptr{Void}, (Ptr{SVMProblem},
         Ptr{SVMParameter}), problem, param)

-    model = SVMModel(ptr, param, reverse_labels, weight_labels, weights,
+    model = SVMModel(ptr, param, problem, nodes, nodeptrs, reverse_labels, weight_labels, weights,
         size(instances, 1), verbose)
     finalizer(model, svmfree)
     model