added inverse error functions erfinv and erfcinv
Merge pull request #2987 from stevengj/erfinv

add inverse error functions erfinv and erfcinv
make bool arithmetic consistently promote to Int.
fixes Gunnar's issue 5, part of #2980
Merge branch 'master' of github.com:JuliaLang/julia
add a couple more performance tips
fixed incorrect return type in erfinv(Float64) (see #2987)
Merge branch 'master' of git://github.com/JuliaLang/julia
better error message for #2975