initial revision
include modpi etc. in the documentation. Don't export pi-related constants.
for modpi(Int64), we check that the argument converts to a float64 losslessly, and throw an error otherwise.
hardcode pi-related constants. Extend mod2pi, modpi, modpio2 to Ints.
made a few constants const across the file
Define modpi etc. for Float32, Int32, Int64. Add tests.
added math-modpi to runtests.jl, add math-modpi to the repository
more tests, fix typos (and that's why we have tests...)
specify libm library when calling rem_pio2
refactored testcases into one nice little array, no more eval/parse/regex
do NOT add a methods for mod(x,y::MathConst{:π})
added modpi etc. documentation. Updated the example for round() using non-ten basis
mod2pi: remove modpi and modpio2, adding a single function to Base.

This is kind of a painful edit since there's a lot of great work in
here, but it's just too much to add three functions to Base. mod2pi
seems like the most sensible of these functions. If we find that
there is great need for the other versions, we can always resurrect
them in the future by the wonders of git history.
rename: test/math-modpi.jl => test/mod2pi.jl, add to test/Makefile
Merge pull request #4862 from JuliaLang/sk/modpi

pared down mod2pi pull request