Ensure n-ary to_index inlines

[mbauman]

While I had fixed the type instability of to_index in 6a3c173, it stopped inlining even sooner!

This is the right solution — use a recursive n-ary splatted argument list. This fixes #11819 properly. I don't have time to run the test suite locally, but assuming CI passes this is good to go.

[mbauman]

Argh, it seems Win64 still doesn't like this simplification to the Array getindex methods.

[tkelman]

The win64 failure was the timeout that's been happening everywhere (and the latest commit here more-or-less worked for me locally), but I didn't try locally on win32 yet and there's apparently an assertion failure in llvm

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
Assertion failed!
Program: C:\projects\julia\usr\bin\julia.exe
File: /home/Tony/julia32/deps/llvm-3.3/include/llvm/ADT/SmallVector.h, Line 144
Expression: begin() + idx < end()
    From worker 2:       * math                Worker 2 terminated.

[mbauman]

Well, lets see if it happens again. I squashed and added a deprecation (since a few packages had been using this and it was easy to deprecate).

[tkelman]

(initially posted this in the wrong issue, don't triage before coffee)

looks like the win32 problem is legitimate, though different error this time?

exception on 2: ERROR: LoadError: test failed: !(isequal(s.dict.keys,k))
 in expression: !(isequal(s.dict.keys,k))
 in error at error.jl:21
 in default_handler at test.jl:29
 in do_test at test.jl:52
 in include at boot.jl:254
 in runtests at C:\projects\julia\test\testdefs.jl:197
 in anonymous at multi.jl:837
 in run_work_thunk at multi.jl:590
 in anonymous at task.jl:837
while loading C:\projects\julia\test\sets.jl, in expression starting on line 95
    From worker 3:       * replutil             in  10.43 seconds
ERROR: LoadError: LoadError: test failed: !(isequal(s.dict.keys,k))
 in expression: !(isequal(s.dict.keys,k))
 in anonymous at task.jl:1403
while loading C:\projects\julia\test\sets.jl, in expression starting on line 95
while loading C:\projects\julia\test\runtests.jl, in expression starting on line 5

    From worker 2:       * sets                Command exited with code 1

edit: this failure is unrelated, #11890