source-highlight: unbreak by using boost 1.53

One of the tests started failing when boost was bumped from 1.53 to 1.54
(in July). Instead of skipping the tests, fix it by using boost 1.53.
source-highlight: 3.1.6 -> 3.1.7

From NEWS file (version 3.1.7):

  * fixed compilation bugs in MacOsX systems (thanks to
    Trevor Spiteri)
  * language definition for Lilypond (thanks to Federico Bruni)
  * language definition for R statistics programming language
  * language definition for ISLISP (thanks to Christian Jullien)
  * improved Erlang definition file (thanks to Erik Søe Sørensen)
  * new output format: ESC 256 ascii code (thanks to
    Xavier-Emmanuel Vincent).

(It still needs boost 1.53 for all tests to pass.)