This change adds a test suite for libx52util, testing all the positive
cases where a character is added to the lookup table. For now, this test
suite only verifies single character mappings, not double character
mappings. A future commit will add test cases for characters not in the
map.
On some systems (notably FreeBSD), the make implementation makes a
distinction between $(builddir)/<path> and <path>, even when builddir is
`.`. This commit removes $(builddir) from all references to generated
files, so that these implementations don't fail. Keeping $(builddir)
causes older versions automake (1.15 and older) to generate a broken
Makefile.