add a gitignore file.

.gitignore

@@ -0,0 +1,18 @@
+*.o
+Makefile
+config.h
+config.log
+config.status
+images/Makefile
+perl/Makefile
+perl/gpligc
+src/.deps/
+src/Makefile
+src/createworld
+src/etopo1merger
+src/etopo2merger
+src/merger
+src/ogie
+src/optimizer
+stamp-h1
+