new MathConst type: make π, e, and γ instances.

This makes BigInt(2)*pi work as one would want it to. It's limited
though and doesn't try to do anything fancy or symbolic beyond that.
We could add a big function that converts integers to BigInts, and
floats and MathConsts to BigFloats.
MathConst: improve interactions with complex and imaginary values.
big: big(x) turns x into an appropriate high-precision version.
MathConst: factor constant-related stuff into its own source file.
MathConst: `@math_const` macro to setup BigFloat-based constants.
MathConst: add Catalan's constant, `eu` as alias for Euler's e.

Defining big(::MathConst) earlier allows using it various places.
Assert that the value of a MathConst converted to BigFloat is of
type BigFloat.
MathConst: add φ or `golden` for the Golden ratio -- (1+sqrt(5))/2.
Removed comment in Arch section re Windows PATH

I repeated the Arch cross-compilation steps to recheck everything, and noticed that the Windows PATH environment variable does not need to include the Julia lib directory (the Julia batch file executes without needing this additional step), so I removed my relevant comment.
Replace i1mach and d1mach calls
Init Streamer sections. Fixes #3338
Improve static load balancing in @parallel

Ensure that static load balancing is as good as possible: each worker
process gets either M or M+1 elements of the input range.

Also fix a bug in preduce() which could cause a bounds exception when
the length of the input range was smaller than the number of workers.
Test @parallel load balancing and reduction for small ranges
Merge pull request #3339 from c42f/cjf/parfix

RFC: Improve static load balancing in @parallel
Merge pull request #3341 from ihnorton/fix-3338

Init Streamer sections. Fixes #3338
Merge pull request #3330 from scidom/patch-2

Removed comment in Arch section re Windows PATH
fix BUILD_MACHINE to be for the host machine, not the target
ARCH should be for the target CC, not the build machine
fix llvm basic block structure of typeassert
this fixes a verifier failure during Pkg.add()
fix an flisp bug
Allow empty ~/.julia/v0.2 to be initialized and used