👷 added task to check amalgamation #906

- Builds and runs test cases from individual sources rather than from amalgamation.
- Checks whether amalgamation would create the same single-header file as checked in.

.travis.yml

@@ -74,6 +74,20 @@ matrix:
  sources: ['ubuntu-toolchain-r-test']
  packages: ['g++-4.9', 'ninja-build']
 
+ # check amalgamation
+ - os: linux
+ compiler: gcc
+ env:
+ - COMPILER=g++-4.9
+ - SPECIAL=amalgamation
+ - CMAKE_OPTIONS=-DJSON_MultipleHeader=ON
+ addons:
+ apt:
+ sources: ['ubuntu-toolchain-r-test']
+ packages: ['g++-4.9', 'astyle', 'ninja-build']
+ after_success:
+ - make check-amalgamation
+
  # Coveralls (http://gronlier.fr/blog/2015/01/adding-code-coverage-to-your-c-project/)
 
  - os: linux