Cleaned up more precisely after make check.

Cleaned up more precisely after make check.

BUILT_SOURCES is now just the list of headers built as per the
automake manual. We provide the list of files to clean to make
rebuilding the test suite programs easier. We then use the CLEANFILES
list in a dist-hook to clean up the distribution that automake gathers
since not distributing flex generated files is foreign to automake's
mindset, but we need exactly that.

Additionally, we locate inputs to the tables-related tests more
precisely. Some files are in srcdir and some are in builddir, which
the arguments to the log compiler are now made aware of.