Make MVM_radix return an array of integers
small fixes to MVM_bigint_radix
s/MVMnum64/MVMint64/
Preparations for refactoring I/O code.

Adds a table of I/O operations, and starts preparing MVMOSHandle for
working in this way. No functional changes yet.
Start moving sync file I/O to new factoring.

Goes far enough to pass NQP tests and Rakudo sanity tests, though some
pieces are left to move over.
Move the rest of the file I/O into the new place.

Except the logic in MVM_file_read_fhs, which is sufficiently wrong to
just toss and do over.
Refactor file handle case of standard streams.
Clean up most of old file I/O bits.

Still can't quite get rid of fd in MVMOSHandle, as a few more things
need moving first.
Move truncate to new scheme.
Move file lock/unlock code.
Final steps of moving file I/O out.

With this, it's all now encapsulated in syncfile.c, and detangled from
everything else.
Add decode stream mechanism for bytes => chars.

We'll use this for the various kinds of IO we do, allowing us to get
buffers of whatever size in, potentially with characters being over
buffer boundaries, and get chars out correctly. Not perfect, still
some optimization and cleanups to go and no doubt some bugs to find.
Also, only UTF-8 supports decode stream so far.
Switch synchronous I/O over to use decode stream.
bump the cur_page of MVMGen2SizeClass
Correct Latin-1; add Windows-1252.

The Latin-1 implementation we had actually did Windows-1252. We're not
HTML 5, so should actually Latin-1 when asked to. Keep the original
code around as a Windows-1252 implementation.
implement a constant cache for ints 0 to 16
Implement streaming decode for Latin-1 and ASCII.
protect adding new types to int cache with mutex
remove unnecessary safety check/debugging thingie
Assorted DecodeStream fixes and tweaks.

With this, we're back to no regressed spectests in Rakudo for this
branch.