Add benchmark for our DTGBA SAT-minimization.

* bench/dtgbasat/: New directory.
* bench/Makefile.am: New file.
* configure.ac, README: Adjust.

bench/dtgbasat/README

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+These are the benchmark for our submission to VMCAI'14.
+
+To reproduce, follow these instructions:
+
+1) Compile Spot and install if it is not already done.
+
+2) Compile Glucose from https://www.lri.fr/~simon/?page=glucose
+   and make sure the 'glucose' binary is in your PATH.
+
+3) Compile ltl2dstar from http://www.ltl2dstar.de/ and
+   make sure the 'ltl2dstar' binary is in your path.
+
+4) Compile DBAminimizer from
+   http://www.react.uni-saarland.de/tools/dbaminimizer
+
+   and define the path to minimize.py with
+
+   % export DBA_MINIMIZER=$HOME/dbaminimizer/minimize.py
+
+5) Then make sure you are in this directory:
+
+   % cd bench/dtgbasat/
+
+6) Classify the set of formulas with
+
+   % ./prepare.sh
+
+   This will read the formulas from file "formulas" and output a file
+   "info.ltl", in which each formula is associated to a class (the ①,
+   ②, ②, and ④ of the paper), and a number of acceptance conditions
+   (the "m" of the paper).
+
+7) Build a makefile to run all experiments
+
+   % ./stats.sh
+
+8) You may optionally change the directory that contains temporary
+    files with
+
+   % export TMPDIR=someplace
+
+   (These temporary files can be several GB large.)
+
+   Note that runtime will be limited to 2h, but memory is not bounded.
+   You should set such a limit with "ulimit" if you like.  For instance
+   % ulimit -v 41943040
+
+9) Actually run all experiments
+
+   % make -j4 stat.mk
+
+   This will build a CSV file called "all.log".
+
+10) You may generate LaTeX code for the tables with the scripts:
+   - tabl.pl: Full data.
+   - tabl1.pl, tabl2.pl, tabl3.pl, tabl4.pl: Partial tables as shown
+   in the paper.
+
+   All these script takes the CSV file all.log as first argument, and
+   output LaTeX to their standard output.
+
+
+For more instruction about how to use ltl2tgba and dstar2tgba to
+compute minimal DTGBA or DTBA, please read doc/userdoc/satmin.html