Fix error in Array.prototype.toString().

Fix use-after-free in regexp source property access.

The underlying string of the "source" property of a regular expression
object can be freed if the regexp is garbage collected.

This could lead to a use-after-free, because the accessor incorrectly
assumed that the regexp source was an interned (thus never freed) string.
Fix this by calling js_pushstring instead of the faster but unsafe
js_pushliteral.

Many thanks to Connor Nelson for spotting this!

Prevent negative table indexing in js_strtol

Support externally set CFLAGS, CPPFLAGS, and LDFLAGS.

Issue #141: Add missing end-of-string checks in regexp lexer.

Fix type error in jsdate.js InLeapYear that led to bad calculations.

InLeapYear was passing the time in millis as an integer, which lead to
overflow errors and wrong results.

Fix potential memory corruption when jsV_newmemstring fails to allocate.

Don't change the value until the allocation has succeeded.

Issue 102: Fix ASAN build when using GCC.

GCC's address sanitizer sets the __SANITIZE_ADDRESS__ macro instead.

Fix gcc compiler warnings about switch fallthroughs.

Fix issue 66: Stack overflow when compiling long regexp sequences.

The syntax tree for long chains of Cat nodes leaned leftwards, which
made the compile() step potentially run out of stack. If we build the
Cat tree leaning right, we can use an iterative loop instead of
recursion.