Travis: check that the project compiles by including everything

and completely ignoring the normal autotools way.

This is completely unsupported, but some projects use it that
way no matter what.

.travis.yml

@@ -11,6 +11,7 @@ compiler:
 
 before_script:
  - ./autogen.sh
+ - ( echo '#include <sodium.h>' ; echo 'int main(void) { return sodium_init(); }' ) > /tmp/main.c && gcc -Isrc/libsodium/include -Isrc/libsodium/include/sodium $(find src -name '*.c' -o -name '*.S') /tmp/main.c
 
 script:
  - ./configure --disable-dependency-tracking