This patch enables correct compilation on both MacOS and Linux using only
POSIX.1-2008-compliant C with XSI extensions.
Specifically, POSIX.1-2008 is the minimum version because we use strdup(3);
explicit XSI is required to expose putenv from glibc.
- travis now tests the packaged source to detect missing source/headers
- basic tests are less sensitive to the directory from where they are run
- fixed some missing files from the `make dist` manifest
- updated the format of NEWS to work with `make dist`