Control NaN injection by library (plus some misc. tweaks)

[ashton314]

Major changes

• Add option to inject only in certain modules (has issues; see #1)
• Log files now start with a timestamp to facilitate multiple runs of a test suite

Discussion

I've updated the FloatTrackerExamples repository for the n-body example. In revision a721f17, I wrote:

N-body example now only injects NaNs inside of the NBodySimulator and OrdinaryDiffEq libraries—testing showed that NBodySimulator doesn't actually do any work with floating point values; instead it pushes all the work off onto OrdinaryDiffEq.

The N-body example seems to work pretty well and consistently now, which is awesome!

Taylor said that calling stacktrace() is an expensive function; I've worked to make sure stacktrace() is called as late in the decision process as possible, so as soon as all NaNs to inject have been used up, stuff should speed up.

[bennn]

@ashton314 I don't see the updates in FloatTrackerExamples. Needs a push?

[ashton314]

@bennn oops—fixed

[ashton314]

@tcallred I've opened issue #3 to track adding benchmarks. Help on this would be appreciated.