Updating `reject` and `summarize_stat_samples`.

For `reject` function, appending `const` to the types of all input
variables that are not modified in the function.

Also, adding an assert to `summarize_stat_samples` to check if the
`sample_sum_array` passed in is of the correct length.
Adding more tests.

Adding `check_eureject.c` which tests functions and types in
`eureject`.c/h. Updating `test/Makefile.am` accordingly.

Also, adding several test data files.
Updating `test/Makefile.am`.

Adding new data files to the list of files to distribute but not
install.

Code is currently passing all `make check` tests and is also
passing `distcheck`.