Rename tgbatest into tests.

* src/Makefile.am, README, configure.ac: update references.
* src/tgbatest/: rename as...
* src/tests/: ...this!

src/tests/.gitignore

@@ -0,0 +1,41 @@
+acc
+bddprod
+bitvect
+blue_counter
+checkpsl
+checkta
+complement
+defs
+.deps
+*.dot
+eltl2tgba
+emptchk
+expldot
+explicit
+explicit2
+explicit3
+explprod
+input
+intvcomp
+intvcmp2
+.libs
+ltl2tgba
+ltlmagic
+ltlprod
+Makefile
+Makefile.in
+maskacc
+mixprod
+output1
+output2
+powerset
+*.ps
+randtgba
+readsat
+readsave
+reduccmp
+reductgba
+spotlbtt
+taatgba
+tgbaread
+tripprod