makeonecross: Make a cross from two solutions and mutate.
In STPGA: Selection of Training Populations by Genetic Algorithm

Given two training sets, identifiers for candidates, this function makes a new solution using crossover and one point mutation with probability mutprob. Only one mutation is allowed.

1	makeonecross(x1, x2, Candidates, mutprob, mutintensity=2)

`x1`	a vector of identifiers selected from the candidate set.
`x2`	a vector of identifiers selected from the candidate set that has the same length as x1.
`Candidates`	vector of identifiers for individuals in the candidate set.
`mutprob`	point mutation probability for each individual generated. Only one mutation per solution is allowed.
`mutintensity`	mean of the poisson variable that is used to decide the number of mutations for each cross.