AST: deallocate nodes

Use a bumpptr allocator to keep track of the AST nodes.
I could not use the LLVM one because it does not call the destructor on allocated elements.

AST & BST: remove unnecessary nodes and fields + little less memory usage

This reverts commit 111ca525.

BST: a bytecode-like AST

And make BST_arguments a bit safer by removing misleading fields.

And remove some extraneous things from bst

fix a bug where compare could ignore CAPI exceptions and add _heapq

A bunch of function metadata refactorings

since this is where it's supposed to live.  The function ctor
copies these fields from the code object.

Instead, merge it into BoxedCode.  This way we'll get refcounting
of our codegen datastructures.

I didn't do anything more than inline all of FunctionMetadata's fields
into BoxedCode, and then delete the FunctionMetadata object.

Revert "Merge pull request #1349 from kmod/scoping"

This reverts commit 2783ab4e, reversing
changes made to ea8890e8.

Let Pyston compatible with GCC 5.x

I think we don't need libunwind to generate doc. And libunwind will call
latex2man and pdflatex to generate its doc. And this can not be disabled
through command line. Please see here: https://bugzilla.mozilla.org/show_bug.cgi?id=738302

When update to gcc 5.4, it complain there has no
has_trivial_copy_constructor, please see here: http://www.chpc-tech.com/EN/NewDevelopments/2015/15.04.23.gcc5.1.html
So use standard c++ 11 type traits.

GCC 5.4 will report those type castings are not legal.

Create all FunctionMetadatas for a module at once

There are a bunch of interrelated changes in here that I couldn't really
separate out.  Mostly the relate to saving data on the AST nodes: we store
DerefInfo and closure info on the Name nodes, and store FunctionMetadata objects
on AST nodes that create scopes.  And those FunctionMetadata objects now also
store "ScopingResults", which is only the results from the ScopeInfo objects,
not all the extra info those keep around in order to do deferred analysis.

Once all this extra data is precomputed+stored, we can start freeing
the ScopingAnalysis objects and all the related ScopeInfos.

Future work:
- Name node shouldn't store scoing info; this should be embedded in choice of BST nodes
- Do pyc caching post-CFG
- Memory management.
- Continue to clean this all up.  I layered this change on top of the existing
  scoping and cfg systems, which reduced the amount of changes, but means that
  there is a potentially-unnecessary layer in the middle now.

microptimizations: use DEFAULT_CLASS_SIMPLE, non gc code object, fewer handleFrameExit calls 

by decrefing frame_info->exc earlier this will less often be true:
if (frame->ob_refcnt > 1)
    frame->handleFrameExit();

Turn off implicit-function check in release mode

I think it'd be nicer to just abort() like we do here, but
cffi is actually testing this behavior (that loading an invalid
library causes an ImportError).

This is being exposed now because before, the library would fail
to compile due to -Werror=implicit-function-declaration and not even
get to the loading step.

I'm still hoping that we can keep this on in some way, because it continues to find issues.
So let's try keeping it on for debug builds.

I'm not sure if this is weakening the check enough (there may be other cases like scipy),
but it's sounding like we need to have this check turned off in our releases regardless,
such as issue #1344.

Fix leak check after path changes

this check is not very robust :-(