assertion facilities

A few macros that I'm tired of copy-pasting from project to project,
so now they will end up in /usr/local/include/rvutils/ass.h for easy
inclusion.
tmppool: pool of initialized objects

The GMP manual suggests that one avoids "excessive initializing and
clearing of variables". Most functions built on top of the GMP library
do need some auxiliary storage, so the only way to avoid
initialization and clearing on each function call is to have a pool of
initialized mpz/mpq variables. (Using static variables would either
kill thread safety or force serialization of each function call; also,
using a common pool saves memory, since the various functions get to
reuse each other's tmp variables).

I decided to rip out the pool management code into a small
library. Hopefully, clang will some day support initialization of a
flexible array member.
Prepare for adding proper tests

I will start adding tests of the various utilities, so this adds a
test harness. This might be overkill, but I don't feel like
reinventing the wheel.
Add .gitignore file

and ignore the test-results directory.
Add trivial test script
Add test data set

Some of the utilities will require somewhat large data sets to do a
realistic test.

This data set is downloaded from
http://www.theguardian.com/news/datablog/2010/feb/11/winter-olympics-medals-by-country
and then converted to a tab-separated text file.
tmppool: Fix embarrasing wrong assert

The condition was inverted (I was probably confused by BUILD_BUG_ON
having the opposite semantics of static_assert).
install: Also install programs

Install the programs quickstat, split_col and cumufreq.
split_col: Add test script

This tests various aspects of the split_col utility.

TBD: Also test the EMFILE/ENFILE handling.