Changed method finding func

The earlier method of finding func was incomplete. This new method is more robust and less likely to fail. This method is still in progress.
func modification to solve nonlinear sysode of 2 eq order1 type5

Earlier there was error comming in solving the type 5 of nonlinear sysode of 2 equations due to problem in function returned which was `[y(t), y(t)]`. This commit contain modification such as to remove that error. This also places the @XFAILed test back to normal.
Replaced `func` with `funcs` and vice versa

At some places func was used for many functions and funcs was used for single function. This commit replaces that in classify_sysode
Corrected comment
Merge pull request #7738 from KDMOE/func_order

Changed method for finding functions fixes #7723 fixes #7736