Update the measure_loc.py tool to use a sampling profiler
Set lineno on these constructed AST nodes
Nuke the old llvm interpreter
Turn on LLVM's "basic regalloc" by default

Can still switch back to the default regalloc using the -b flag,
but it looks like the basic register allocator cuts the LLVM JIT
time significantly, and improves every one of our benchmarks.
Refactor interpreter slightly in preparation for resume-at-any-point

Previously things were hardcoded to only allow a single entry point to
the interpreter (since that is how the unwinder determines if the frame
is an interpreter frame).

Instead of having astInterpretFunction be the interpreter frame, make
execute() the frame.  Have to make it a static class function so we can
take its address.
Had to do this for 14.04

I wonder if other people have run into this.
Rename ExcInfo -> UnwindInfo

and exc_info -> unw_info

(This makes more sense with the next change, but I wanted
to separate this large renaming from the functional change.)
Change the way we pass line numbers to the runtime

Before, for compiled functions we used dwarf line number information.

Now it's switched to using the new frame introspection support, and
we pass through the AST_stmt* as one of the arguments.  This gets us
the line number and also the definition of execution point.
And we come full circle -- this seems like the right solution but we moved away from it?
Refactor some common control-flow-creation code (NFC)
Have the tool output some partial stats
Fix a bug in OSR-entry guard checking

If we had to guard on the type of an object but the variable
ended up being undefined, we treated that as a guard failure
(not sure why).

Fixing that exposed another issue: if we guard that an object
is an int, we will try to unbox it if necessary.  If the variable
wasn't defined, then we will try to unbox some garbage memory.
Use the new handlePotentiallyUndefined to deal with that.
Ressurect the C-extension tracing measure_loc
Minor measure_loc improvements
Forgot to add this
Should check this at the end to at least identify the issue rather than giving bogus results