Add .gitignore everywhere based on .cvsignore.

* .gitignore: New.
* build-aux/.gitignore: New.
* data/.gitignore: New.
* doc/.gitignore: New.
* etc/.gitignore: New.
* examples/.gitignore: New.
* examples/calc++/.gitignore: New.
* lib/.gitignore: New.
* m4/.gitignore: New.
* po/.gitignore: New.
* runtime-po/.gitignore: New.
* src/.gitignore: New.
* tests/.gitignore: New.

build-aux/.gitignore

@@ -0,0 +1,16 @@
+/Makefile
+/Makefile.in
+/compile
+/config.guess
+/config.rpath
+/config.sub
+/depcomp
+/git-version-gen
+/install-sh
+/javacomp.sh.in
+/javaexec.sh.in
+/link-warning.h
+/mdate-sh
+/missing
+/texinfo.tex
+/ylwrap