Upgrade Twig to 1.15.* from 1.12.*

Updated: Comment #N

Problem/Motivation

There has been some improvements that would help autoescape compiling about 20% faster. And a bunch of bug fixes for auto-escape and UTF strings.

Change Log Diff:

* 1.15.0 (2013-12-06)

 * made ignoreStrictCheck in Template::getAttribute() works with __call() methods throwing BadMethodCallException
 * added min and max functions
 * added the round filter
 * fixed a bug that prevented the optimizers to be enabled/disabled selectively
 * fixed first and last filters for UTF-8 strings
 * added a source function to include the content of a template without rendering it
 * fixed the C extension sandbox behavior when get or set is prepend to method name

* 1.14.2 (2013-10-30)

 * fixed error filename/line when an error occurs in an included file
 * allowed operators that contain whitespaces to have more than one whitespace
 * allowed tests to be made of 1 or 2 words (like "same as" or "divisible by")

* 1.14.1 (2013-10-15)

 * made it possible to use named operators as variables
 * fixed the possibility to have a variable named 'matches'
 * added support for PHP 5.5 DateTimeInterface

* 1.14.0 (2013-10-03)

 * fixed usage of the html_attr escaping strategy to avoid double-escaping with the html strategy
 * added new operators: ends with, starts with, and matches
 * fixed some compatibility issues with HHVM
 * added a way to add custom escaping strategies
 * fixed the C extension compilation on Windows
 * fixed the batch filter when using a fill argument with an exact match of elements to batch
 * fixed the filesystem loader cache when a template name exists in several namespaces
 * fixed template_from_string when the template includes or extends other ones
 * fixed a crash of the C extension on an edge case

* 1.13.2 (2013-08-03)

 * fixed the error line number for an error occurs in and embedded template
 * fixed crashes of the C extension on some edge cases

* 1.13.1 (2013-06-06)

 * added the possibility to ignore the filesystem constructor argument in Twig_Loader_Filesystem
 * fixed Twig_Loader_Chain::exists() for a loader which implements Twig_ExistsLoaderInterface
 * adjusted backtrace call to reduce memory usage when an error occurs
 * added support for object instances as the second argument of the constant test
 * fixed the include function when used in an assignment

* 1.13.0 (2013-05-10)

 * fixed getting a numeric-like item on a variable ('09' for instance)
 * fixed getting a boolean or float key on an array, so it is consistent with PHP's array access:
   `{{ array[false] }}` behaves the same as `echo $array[false];` (equals `$array[0]`)
 * made the escape filter 20% faster for happy path (escaping string for html with UTF-8)
 * changed ☃ to § in tests
 * enforced usage of named arguments after positional ones

Proposed resolution

Update Twig to 1.15.* from 1.12.*

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Follow-up from #1825952: Turn on twig autoescape by default.