possible deSolve issue

Ran into an interesting issue during testing - I don't think this should be Bayes specific, but this is the code I ran and the error message I got:

``` r
sp <- function(split_dates) { replace(
specs(mm_name('bayes', err_proc_iid=FALSE),
n_cores=3, n_chains=3, burnin_steps=300, saved_steps=100, verbose=FALSE),
'split_dates', split_dates
) }
dat <- data_metab('1', res='30')
mm <- metab(sp(split_dates=FALSE), dat)
mm <- metab(sp(split_dates=TRUE), dat)
dat <- data_metab('3', res='30')
mm <- metab(sp(split_dates=FALSE), dat)
mm <- metab(sp(split_dates=TRUE), dat)
## Error in .Call("call_rkFixed", as.double(y), as.double(times), Func, Initfunc, :
## "call_rkFixed" not resolved from current namespace (deSolve)
## Error in .C("unlock_solver") :
## "unlock_solver" not resolved from current namespace (deSolve)
```

Sometimes it breaks on the third `metab()` call, sometimes on the fourth. It occurs whether I've compiled the stan code during this R session or a previous one.

From then on, I get the same error message anytime I try to run any Bayesian model, though an MLE works fine:

``` r
mm <- metab(sp(split_dates=FALSE), dat)
## Error in .Call("call_rkFixed", as.double(y), as.double(times), Func, Initfunc, :
## "call_rkFixed" not resolved from current namespace (deSolve)
## Error in .C("unlock_solver") :
## "unlock_solver" not resolved from current namespace (deSolve)

mm <- metab(specs('mle'), dat)
mm
## metab_model of type metab_mle
## [etc.]

mm <- metab(sp(split_dates=FALSE), dat)
## R session aborted
```

See
http://r.789695.n4.nabble.com/deSolve-unresolved-namespace-error-td4679888.html: The solution may be to call library(deSolve) before loading/running streamMetabolizer. But I don't want to add a CRAN-breaking code line (`library()`) until I'm sure it's necessary, so I'm waiting and just adding this issue for now.

Start by reproducing the repeated metab() calls and the deSolve namespace errors, then compare behavior with and without library(deSolve) before loading or running streamMetabolizer. Inspect the Bayesian metab path and deSolve interaction; done means identifying the cause and documenting or testing a project-safe resolution without assuming that library() is appropriate.

Written by the indexing model from the issue text.