Require cmake >= 2.8.9, use a ppa for travis.

`package_find(PythonInterp)` doesn't find python 3.2 with the
cmake travis provides.

.travis.yml

@@ -3,8 +3,10 @@ compiler:
  - clang
  - gcc
 before_install:
+ # we need a more recent cmake than travis provides (at least 2.8.9):
+ - echo "yes" | sudo add-apt-repository ppa:kalakris/cmake
  - sudo apt-get update -qq
- - sudo apt-get install -qq python3 pandoc re2c valgrind
+ - sudo apt-get install -qq cmake python3 pandoc re2c valgrind
 script:
  - make testtarball
  - PROG=`ls cmark-*.*/build/src/cmark` make leakcheck

CMakeLists.txt

@@ -1,5 +1,5 @@
 project(cmark)
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 2.8.9)
 
 if("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
     message(FATAL_ERROR "Do not build in-source.\nPlease remove CMakeCache.txt and the CMakeFiles/ directory.\nThen: mkdir build ; cd build ; cmake .. ; make")