Enable precompilation

[jgoldfar]

No description provided.

[ViralBShah]

@tkelman Is this still the preferred way to do the precompliation?

[tkelman]

Either this or isdefined(Base, :__precompile__)

Using isdefined has the benefit that it would work on NO_GIT builds of older 0.4-dev where version numbers are not accurate, but that's probably a rare case.

[acroy]

Certainly nice to have! I don't have a strong preference, which version we should use, but Tony's looks more elegant ...

[jgoldfar]

Good to know; I'll update the PR. I would note that Compat.jl does it this way, so it may be worth updating that as well

[tomasaschan]

isdefined has the added benefit of being forwards compatible, in case the mechanism for precompilation is changed in a future version of Julia (at least in the sense that nothing will throw errors; precompilation will silently break, but that won't make the package unusable).

[jgoldfar]

Test for when to enable precompilation is now updated.