moved copy subset example of string features into a unit test
added a nicer error message
fixed a memory leak by using SGVector instead of array
-removed print_kernel_matrix
-added some error messages
-FIXED A BUG WHICH CAUSED SUBSET INDEX CONFUSION (nasty one)
new unit test for subset copying behaviour (fixed bug and this is a test for it)
replaced asserts by expect equal
added example/test for a SVM on string data with a string kernel and a precomputed kernel matrix which are asserted to return the same predictions
added some comments on the MMD examples and the custom kernel bugfix
Merge branch 'mmd_kernel_selection'
Merge pull request #900 from karlnapf/master

Fixed a serious CustomKernel subset related bug