Replace std.uni in phobos with new version

Fixes some issues in std.string and std.json
adds workarounds to make it work with current DMD

Also add to{Lower,Upper}InPlace, and other minor enhancements since review
few tweaks to aid std.string/std.uni symbiosi:s
fixup 64bit unittest
slice out test to see where does it fails

remove misleading comment

debuging prints for auto-tester
workaround new retro bug 10499
re-write expr to see if it's an optimizer bug on FreeBSD?
revert mass-rename, we have module system
make sure internal helpers are private

and remove a stray debug version
some stray public --> private, package
try to help DMD optimizer, reduce redundancy