Ensure that HAVE_STRNDUP is defined in C
Generate config.h in build tree

- Generate config.h in build tree, rather than source tree.
- Remove ignore for include/config.h, now that we are no longer
  generating it within the source tree.
Merge pull request #197 from justfalter/fix_strndup

Ensure that HAVE_STRNDUP is defined in C, generate config.h in build tree