got things to the point where they build.
Fix selfhosted code to match new API for ForkJoin.
Add assertion to catch a case early that I am dealing with and might also indicate miscompiled code.
fixes ParallelArray to the point where I can construct a Matrix.
checkpoint.

(also, includes later fix alpha-rename bug leftover post-rebase.)

builds and runs expressions like:

    new Matrix([1000], (x,y) => x+1, {spew:1})

or:

    new Matrix([10,10], (x,y) => x+y+1)

but it seems like it is bailing out too eagerly, i.e. even on simple
expressions like the two above.  Blame game via

    (gdb) set env PAFLAGS full
    (gdb) set env IONFLAGS trace

says that possibly self-hosted:4082

         computefunc(indexStart, indexEnd); // in constructSlice

or self-hosted:4148

  function fill2_leaf(indexStart, indexEnd) {

or self-hosted:4149

    var alb = ArrayLikeToString(buffer);

is to blame.  not sure, handing off to shu to poke at.
Alpha-rename pmap et al to mapPar etc.
fix bugs in cursor code -- we need a grain even in the leaves at least for now.
Fix oversight in MatrixCommonMap, which needs to propagate the outptr cursor.
Crazy hacks to get more context during Parallel Bailout failures.

Braindump follows:

As a reminder, here is the usual way Felix has been invoking the js shell:

  TERM=xterm-color PAFLAGS=full IONFLAGS=bailouts ./js

and here is the test case Felix has been using most often:

  (new Matrix([100], ["int32"], function (i) { return i+1; }, {spew:1})).shape

though he has at times varied the size of the shape {10,100,1000}, and
of course toggled the `{spew:1}` argument on and off.

Pushing to github to share with Shu to debug why we are seeing:

  warning: Bailed out of parallel operation: unsupported ArgumentChecks_0 at self-hosted:4104

although we have seen various other scary things such as:

  [Parallel:M]   COMPILE 10316cf38:self-hosted:4072
  [Parallel:M]   END can't compile

potentially in tandem with the addition of a (this === undefined)
condition to a predicate somewhere.
one last crazy hack that wont get approved later.