Fix default value text for ReflectionFunction

The escaping used by outputPHP produces valid PHP, but it is
sometimes a string concatenation expression which can't be directly
substituted in as the default value of a function. This diff adds a
new mode to VariableSerializer that will always output a single string
literal for string values.
Fix expected string for TestHint

A previous diff made a couple changes to the text returned from
ReflectionFunction::getDefaultValueText() (it now returns
double-quoted strings and uppercase NULL constants). I forgot to
update TestHint which tests this.
Don't emit FCallBuiltin for redefinable builtins

We were emitting FCallBuiltin at emit time for "idx", but were
resolving "idx" to the user-defined function at runtime.
Remove a bunch of unnecessary double-semicolons

I saw these in ir.h and found a few more with git grep.
Use delete (not free) for deallocating new'd memory.

A few random places where blocks are being allocated
with new, but deallocated with free.
Make SIMPLIFY_CMP not a macro

Made it easier to debug/edit this function.
Add libdouble-conversion to third_party
Add folly to third_party
Tweaks to IR trace printing

Indents the IR and assembler output more than the respective
previous representations (seems easier to understand than outdenting
things relative to the HHBC).  Also fixes support for ostreams other
than std::cout and get rid of the php-source line numbers.
Remove need for cgFoo functions to return their start address

Remove some boilerplate.  Also most functions (top-level IR
instructions) seem to be intended to have the semantics that emitting
no code returns null, while many helpers just returned the frontier.
This lead to some cases (e.g. cgLdStack, cgStMem, etc) having
different semantics from other instructions.
Update system generated files and fix generator scripts
Make HHIR returns a little more like tx64 returns

Adds and modifies few IR instructions so that the generic
return case can use the tx64 freeLocalsHelpers.
Fix TestCodeRun-Hint

hphpc and hhvm have different code for generating the default
value text used in reflection. This updates hphpc to be consistent
with hhvm.
Add class name to symbols in perf-.pid.map
Factor out tvRefcountedDecRef/IncRef where possible.

Use helpers where we can.  Introduced new helpers to aid fast-path/cold-path code that checks to see if a destructor will be called before doing a decref.
DebugInfo cleanup
Don't populate 'args' array in backtrace frames in RepoAuthoritative mode

hphp has been doing this for ages and a number of internal
tools rely on this behavior. hhvm is now consistent with hphp.
A few minor cleanup tweaks, mostly Translator::analyze related

Some minor comment tweaks to make them closer to truth; add
some missing header dependencies; return unique_ptr<Tracelet> and take
SrcKey by value; move stackFrameOffset to not be a member variable;
and remove some uses of Transl::curFunc from the IR.
allocRegsForTrace doesn't actually need a TraceBuilder

Remove unused parameter.
Remove some dead AllocActRec code in codegen.cpp

We only use the 6-argument version of AllocActRec now.