Better error message for using old Problem creation notatio

[TorkelE]

With v10 coming out there will probably be tons of people using the old notation to create ODEProblems by mistake (i.e. I did for a while until I looked at the NEws file). It might make sense to add a specific warning mentioning the v10 release. It will likely save people tons of time.

Currently

using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D

@parameters p d1 d2
@variables X(t) Y(t)

ode_eqs = [
    D(X) ~ p - d1*X,
    D(Y) ~ p - d2*Y
]
@mtkcompile osys = System(ode_eqs, t)

u0 = [X => 0.2, Y => 2.0]
tspan = (0.0, 10.0)
ps = [p => 1.0, d1 => 0.5, d2 => 1.0]
oprob = ODEProblem(osys, u0, tspan, ps)

yields a

ERROR: No methods were found for the model function passed to the equation solver.
The function `f` needs to have dispatches, for example, for an ODEProblem
`f` must define either `f(u,p,t)` or `f(du,u,p,t)`. For more information
on how the model function `f` should be defined, consult the docstring for
the appropriate `AbstractSciMLFunction`.

Offending function: f
Stacktrace:
 [1] 
   @ SciMLBase ~/.julia/packages/SciMLBase/Ha7rZ/src/utils.jl:254
 [2] isinplace (repeats 2 times)
   @ ~/.julia/packages/SciMLBase/Ha7rZ/src/utils.jl:246 [inlined]
 [3] ODEProblem(f::System, u0::Vector{Pair{…}}, tspan::Tuple{Float64, Float64}, p::Vector{Pair{…}}; kwargs::@Kwargs{})
   @ SciMLBase ~/.julia/packages/SciMLBase/Ha7rZ/src/problems/ode_problems.jl:198
 [4] ODEProblem(f::System, u0::Vector{Pair{Num, Float64}}, tspan::Tuple{Float64, Float64}, p::Vector{Pair{Num, Float64}})
   @ SciMLBase ~/.julia/packages/SciMLBase/Ha7rZ/src/problems/ode_problems.jl:197
 [5] top-level scope
   @ ~/Desktop/Julia Playground/Environment - Temporary/temporary_playground.jl:23
Some type information was truncated. Use `show(err)` to see complete types.

error, which is not very helpful.

[ChrisRackauckas]

Yeah just saw this in the OrdinaryDiffEq tests, definitely not intended.