pkg2/resolve: add prerelase/build in VersionWeigth

this will allow to remove filtering of prerelease/build versions,
and "normalization" of packages requirements which was introduced
in 0fa84ec69f060cc492772b1a1707eff3745675bf
pkg2: reinstate prerelease/build versions

Prerelease/build versions can again be used in "require" files.

This essentially reverts commits
0fa84ec69f060cc492772b1a1707eff3745675bf
923e385d029b22df67739f7f1de6df18721d2f97
pkg2: more tests in resolve2

For the new weighting scheme. Also, sanitize previous
tetst a little.
Show  build status for packages which have travis integration
Put libuv back to proper hash
Bump Rmath
Merge branch 'master' of github.com:JuliaLang/julia
split sys0.ji into a separate build rule (approximately revert
8044eb16351dcc66bd952c684b42069585944489)

this gives us better visibility into partial build failures, provides a backup sys.ji file, and simplifies the build rules somewhat
Improve on functionality for matrices with zero dimensions
Merge pull request #3853 from JuliaLang/anj/zerodim

Improve on functionality for matrices with zero dimensions
Merge pull request #3921 from aviks/pkg-travis

RFC: Show  build status for packages which have travis integration
fix #3916
fix #3915
fix #3638
Fix Intel libm path.
Some more updates for libimf usage
Clarify reinterpret() in docs
fix length(::MethodTable)
doc: update helpdb & UNDOCUMENTED
Add info on editing documentation to CONTRIBUTING.md