Use atsign-simd for sum
reworked cluster manager interface
check integer truncation (#5413) and make more operators follow T+T => T (#3759)

the sysimg builds, but still need to:
  - check same-size signed<->unsigned conversion
  - make tests pass
get numbers test passing with checked integer conversions and type-stable arithmetic
make a couple things safe for checked signed<->unsigned conversion
check signed<->unsigned conversions

this would be a bit cleaner without the code in intfuncs that dispatches
on Unsigned.

signed() and unsigned() are convenient for testing bit patterns in the
test suite. for now replace with assigned() and asunsigned().

uint8(x) is convenient for moving bytes around, so it remains unchecked.
we should perhaps rename this to byte(), and either eliminate uint8()
entirely, or make it checked.
get dates tests passing with checked signed<->unsigned conversion
Merge branch 'master' of github.com:JuliaLang/julia into jb/checked_int_trunc

Conflicts:
	base/number.jl
get a few more things working with checked integer conversions
allow x[i,j;k] syntax to be parsed #7225
Apply custom keymaps to all prompt modes and document it.
Modify fixup-libgfortran so it works on Linux as well
Move fixup-libgfortran to `contrib/`, enable it for Linux as well as OSX
Add developer documentation for :meta expressions
First draft
WIP
Type inference works correctly
Remove left over caddddr
Fix Splatting
Ugly version of error handling

This will have to be changed once we switch the way we do func_for_method,
but I will await @JeffBezanson's judgement on how to do that best, so I'll
use this to go head first.